Intro to Raster Data

Last updated on 2024-03-12 | Edit this page

Estimated time: 50 minutes

OUTPUT

phantomjs has been installed to /home/runner/bin

WARNING

Warning in
download.file("https://www.naturalearthdata.com/http//www.naturalearthdata.com/download/110m/physical/ne_110m_graticules_all.zip",
: cannot open URL
'https://www.naturalearthdata.com/http//www.naturalearthdata.com/download/110m/physical/ne_110m_graticules_all.zip':
HTTP status was '500 Internal Server Error'

ERROR

Error in download.file("https://www.naturalearthdata.com/http//www.naturalearthdata.com/download/110m/physical/ne_110m_graticules_all.zip", : cannot open URL 'https://www.naturalearthdata.com/http//www.naturalearthdata.com/download/110m/physical/ne_110m_graticules_all.zip'

Overview

Questions

  • What is a raster dataset?
  • How do I work with and plot raster data in R?
  • How can I handle missing or bad data values for a raster?

Objectives

  • Describe the fundamental attributes of a raster dataset.
  • Explore raster attributes and metadata using R.
  • Import rasters into R using the terra package.
  • Plot a raster file in R using the ggplot2 package.
  • Describe the difference between single- and multi-band rasters.

Things You’ll Need To Complete This Episode

See the lesson homepage for detailed information about the software, data, and other prerequisites you will need to work through the examples in this episode.

In this episode, we will introduce the fundamental principles, packages and metadata/raster attributes that are needed to work with raster data in R. We will discuss some of the core metadata elements that we need to understand to work with rasters in R, including CRS and resolution. We will also explore missing and bad data values as stored in a raster and how R handles these elements.

We will continue to work with the dplyr and ggplot2 packages that were introduced in the Introduction to R for Geospatial Data lesson. We will use two additional packages in this episode to work with raster data - the terra and sf packages. Make sure that you have these packages loaded.

R

library(terra)
library(ggplot2)
library(tidyterra)
library(dplyr)

Introduce the Data

If not already discussed, introduce the datasets that will be used in this lesson. A brief introduction to the datasets can be found on the Geospatial workshop homepage.

For more detailed information about the datasets, check out the Geospatial workshop data page.

View Raster File Attributes


We will be working with a series of GeoTIFF files in this lesson. The GeoTIFF format contains a set of embedded tags with metadata about the raster data. We can use the function describe() to get information about our raster data before we read that data into R. It is ideal to do this before importing your data.

R

describe("data/landsat_casco/b10_cropped/LC09_L2SP_011030_20230920_20230922_02_T1_ST_B10.TIF")

OUTPUT

 [1] "Driver: GTiff/GeoTIFF"                                                                                                                                                                                                                                                                                                                          
 [2] "Files: data/landsat_casco/b10_cropped/LC09_L2SP_011030_20230920_20230922_02_T1_ST_B10.TIF"                                                                                                                                                                                                                                                      
 [3] "Size is 1128, 1349"                                                                                                                                                                                                                                                                                                                             
 [4] "Coordinate System is:"                                                                                                                                                                                                                                                                                                                          
 [5] "PROJCRS[\"WGS 84 / UTM zone 19N\","                                                                                                                                                                                                                                                                                                             
 [6] "    BASEGEOGCRS[\"WGS 84\","                                                                                                                                                                                                                                                                                                                    
 [7] "        DATUM[\"World Geodetic System 1984\","                                                                                                                                                                                                                                                                                                  
 [8] "            ELLIPSOID[\"WGS 84\",6378137,298.257223563,"                                                                                                                                                                                                                                                                                        
 [9] "                LENGTHUNIT[\"metre\",1]]],"                                                                                                                                                                                                                                                                                                     
[10] "        PRIMEM[\"Greenwich\",0,"                                                                                                                                                                                                                                                                                                                
[11] "            ANGLEUNIT[\"degree\",0.0174532925199433]],"                                                                                                                                                                                                                                                                                         
[12] "        ID[\"EPSG\",4326]],"                                                                                                                                                                                                                                                                                                                    
[13] "    CONVERSION[\"UTM zone 19N\","                                                                                                                                                                                                                                                                                                               
[14] "        METHOD[\"Transverse Mercator\","                                                                                                                                                                                                                                                                                                        
[15] "            ID[\"EPSG\",9807]],"                                                                                                                                                                                                                                                                                                                
[16] "        PARAMETER[\"Latitude of natural origin\",0,"                                                                                                                                                                                                                                                                                            
[17] "            ANGLEUNIT[\"degree\",0.0174532925199433],"                                                                                                                                                                                                                                                                                          
[18] "            ID[\"EPSG\",8801]],"                                                                                                                                                                                                                                                                                                                
[19] "        PARAMETER[\"Longitude of natural origin\",-69,"                                                                                                                                                                                                                                                                                         
[20] "            ANGLEUNIT[\"degree\",0.0174532925199433],"                                                                                                                                                                                                                                                                                          
[21] "            ID[\"EPSG\",8802]],"                                                                                                                                                                                                                                                                                                                
[22] "        PARAMETER[\"Scale factor at natural origin\",0.9996,"                                                                                                                                                                                                                                                                                   
[23] "            SCALEUNIT[\"unity\",1],"                                                                                                                                                                                                                                                                                                            
[24] "            ID[\"EPSG\",8805]],"                                                                                                                                                                                                                                                                                                                
[25] "        PARAMETER[\"False easting\",500000,"                                                                                                                                                                                                                                                                                                    
[26] "            LENGTHUNIT[\"metre\",1],"                                                                                                                                                                                                                                                                                                           
[27] "            ID[\"EPSG\",8806]],"                                                                                                                                                                                                                                                                                                                
[28] "        PARAMETER[\"False northing\",0,"                                                                                                                                                                                                                                                                                                        
[29] "            LENGTHUNIT[\"metre\",1],"                                                                                                                                                                                                                                                                                                           
[30] "            ID[\"EPSG\",8807]]],"                                                                                                                                                                                                                                                                                                               
[31] "    CS[Cartesian,2],"                                                                                                                                                                                                                                                                                                                           
[32] "        AXIS[\"(E)\",east,"                                                                                                                                                                                                                                                                                                                     
[33] "            ORDER[1],"                                                                                                                                                                                                                                                                                                                          
[34] "            LENGTHUNIT[\"metre\",1]],"                                                                                                                                                                                                                                                                                                          
[35] "        AXIS[\"(N)\",north,"                                                                                                                                                                                                                                                                                                                    
[36] "            ORDER[2],"                                                                                                                                                                                                                                                                                                                          
[37] "            LENGTHUNIT[\"metre\",1]],"                                                                                                                                                                                                                                                                                                          
[38] "    USAGE["                                                                                                                                                                                                                                                                                                                                     
[39] "        SCOPE[\"Engineering survey, topographic mapping.\"],"                                                                                                                                                                                                                                                                                   
[40] "        AREA[\"Between 72°W and 66°W, northern hemisphere between equator and 84°N, onshore and offshore. Aruba. Bahamas. Brazil. Canada - New Brunswick (NB); Labrador; Nunavut; Nova Scotia (NS); Quebec. Colombia. Dominican Republic. Greenland. Netherlands Antilles. Puerto Rico. Turks and Caicos Islands. United States. Venezuela.\"],"
[41] "        BBOX[0,-72,84,-66]],"                                                                                                                                                                                                                                                                                                                   
[42] "    ID[\"EPSG\",32619]]"                                                                                                                                                                                                                                                                                                                        
[43] "Data axis to CRS axis mapping: 1,2"                                                                                                                                                                                                                                                                                                             
[44] "Origin = (398865.000000000000000,4866405.000000000000000)"                                                                                                                                                                                                                                                                                      
[45] "Pixel Size = (30.000000000000000,-30.000000000000000)"                                                                                                                                                                                                                                                                                          
[46] "Metadata:"                                                                                                                                                                                                                                                                                                                                      
[47] "  AREA_OR_POINT=Area"                                                                                                                                                                                                                                                                                                                           
[48] "Image Structure Metadata:"                                                                                                                                                                                                                                                                                                                      
[49] "  COMPRESSION=LZW"                                                                                                                                                                                                                                                                                                                              
[50] "  INTERLEAVE=BAND"                                                                                                                                                                                                                                                                                                                              
[51] "Corner Coordinates:"                                                                                                                                                                                                                                                                                                                            
[52] "Upper Left  (  398865.000, 4866405.000) ( 70d15'36.90\"W, 43d56'37.75\"N)"                                                                                                                                                                                                                                                                      
[53] "Lower Left  (  398865.000, 4825935.000) ( 70d15' 9.45\"W, 43d34'46.27\"N)"                                                                                                                                                                                                                                                                      
[54] "Upper Right (  432705.000, 4866405.000) ( 69d50'19.04\"W, 43d56'51.69\"N)"                                                                                                                                                                                                                                                                      
[55] "Lower Right (  432705.000, 4825935.000) ( 69d50' 0.77\"W, 43d35' 0.04\"N)"                                                                                                                                                                                                                                                                      
[56] "Center      (  415785.000, 4846170.000) ( 70d 2'46.52\"W, 43d45'49.65\"N)"                                                                                                                                                                                                                                                                      
[57] "Band 1 Block=1128x1 Type=Float32, ColorInterp=Gray"                                                                                                                                                                                                                                                                                             
[58] "  Description = SST_F_20230920"                                                                                                                                                                                                                                                                                                                 
[59] "  Min=47.097 Max=80.462 "                                                                                                                                                                                                                                                                                                                       
[60] "  Minimum=47.097, Maximum=80.462, Mean=-9999.000, StdDev=-9999.000"                                                                                                                                                                                                                                                                             
[61] "  NoData Value=nan"                                                                                                                                                                                                                                                                                                                             
[62] "  Metadata:"                                                                                                                                                                                                                                                                                                                                    
[63] "    STATISTICS_MAXIMUM=80.461517333984"                                                                                                                                                                                                                                                                                                         
[64] "    STATISTICS_MEAN=-9999"                                                                                                                                                                                                                                                                                                                      
[65] "    STATISTICS_MINIMUM=47.096858978271"                                                                                                                                                                                                                                                                                                         
[66] "    STATISTICS_STDDEV=-9999"                                                                                                                                                                                                                                                                                                                    

If you wish to store this information in R, you can do the following:

R

casco_b10_2023_info <- capture.output(
  describe("data/landsat_casco/b10_cropped/LC09_L2SP_011030_20230920_20230922_02_T1_ST_B10.TIF")
)

Each line of text that was printed to the console is now stored as an element of the character vector casco_b10_2023_info. We will be exploring this data throughout this episode. By the end of this episode, you will be able to explain and understand the output above.

Open a Raster in R


Now that we’ve previewed the metadata for our GeoTIFF, let’s import this raster dataset into R and explore its metadata more closely. We can use the rast() function to open a raster in R.

Data Tip - Object names

To improve code readability, file and object names should be used that make it clear what is in the file. The data for this episode were collected from Harvard Forest so we’ll use a naming convention of datatype_casco_2023.

First we will load our raster file into R and view the data structure.

R

b10_casco_2023 <-
  rast("data/landsat_casco/b10_cropped/LC09_L2SP_011030_20230920_20230922_02_T1_ST_B10.TIF")

b10_casco_2023

OUTPUT

class       : SpatRaster 
dimensions  : 1349, 1128, 1  (nrow, ncol, nlyr)
resolution  : 30, 30  (x, y)
extent      : 398865, 432705, 4825935, 4866405  (xmin, xmax, ymin, ymax)
coord. ref. : WGS 84 / UTM zone 19N (EPSG:32619) 
source      : LC09_L2SP_011030_20230920_20230922_02_T1_ST_B10.TIF 
name        : SST_F_20230920 
min value   :       47.09686 
max value   :       80.46152 

The information above includes a report of min and max values, but no other data range statistics. Similar to other R data structures like vectors and data frame columns, descriptive statistics for raster data can be retrieved like

R

summary(b10_casco_2023)

WARNING

Warning: [summary] used a sample

OUTPUT

 SST_F_20230920 
 Min.   :47.13  
 1st Qu.:60.04  
 Median :60.57  
 Mean   :60.97  
 3rd Qu.:61.63  
 Max.   :80.35  
 NA's   :50545  

but note the warning - unless you force R to calculate these statistics using every cell in the raster, it will take a random sample of 100,000 cells and calculate from that instead. To force calculation all the values, you can use the function values:

R

summary(values(b10_casco_2023))

OUTPUT

 SST_F_20230920  
 Min.   :47.1    
 1st Qu.:60.0    
 Median :60.6    
 Mean   :61.0    
 3rd Qu.:61.6    
 Max.   :80.5    
 NA's   :766560  

To visualise this data in R using ggplot2, we have two options. First, We can convert it to a dataframe. We learned about dataframes in an earlier lesson. The terra package has an built-in function for conversion to a plotable dataframe.

R

b10_casco_2023_df <- as.data.frame(b10_casco_2023, xy = TRUE)

Now when we view the structure of our data, we will see a standard dataframe format.

R

str(b10_casco_2023_df)

OUTPUT

'data.frame':	755112 obs. of  3 variables:
 $ x             : num  428640 428670 428700 428730 428760 ...
 $ y             : num  4866390 4866390 4866390 4866390 4866390 ...
 $ SST_F_20230920: num  67.1 66.9 66.7 66.6 66.5 ...

We can use ggplot() to plot this data. We will set the color scale to scale_fill_viridis_c which is a color-blindness friendly color scale. We will also use the coord_quickmap() function to use an approximate Mercator projection for our plots. This approximation is suitable for small areas that are not too close to the poles. Other coordinate systems are available in ggplot2 if needed, you can learn about them at their help page ?coord_map.

R

ggplot() +
    geom_raster(data = b10_casco_2023_df, 
                aes(x = x, y = y, 
                    fill = SST_F_20230920)) +
    scale_fill_viridis_c() +
    coord_quickmap()

WARNING

Warning: Raster pixels are placed at uneven horizontal intervals and will be shifted
ℹ Consider using `geom_tile()` instead.
Raster plot with ggplot2 using the viridis color scale
Raster plot with ggplot2 using the viridis color scale

This is somewhat tedious. With the tidyterra package we have another geom - geom_spatraster that deals with rasters loaded by terra. Also, as land is NA in this data, it will plot it quite nicely by default. We’ll also use coord_sf()

R

ggplot() +
    geom_spatraster(data = b10_casco_2023, 
                    aes(fill = SST_F_20230920)) +
    scale_fill_viridis_c() 

OUTPUT

<SpatRaster> resampled to 500778 cells for plotting
Raster plot with ggplot2 using the viridis color scale
Raster plot with ggplot2 using the viridis color scale

This looks great, and is now on the lat/long scale: CRS 4326. That’s because spatial data is always plotted using the coord_sf() coordinate system which defaults to 4326. If we want to show things in another projection, or use the original one, we have to set a datum argument.

R

ggplot() +
    geom_spatraster(data = b10_casco_2023, 
                    aes(fill = SST_F_20230920)) +
    scale_fill_viridis_c() +
  coord_sf(datum = crs(b10_casco_2023, proj = TRUE))

OUTPUT

<SpatRaster> resampled to 500778 cells for plotting
Raster plot with ggplot2 using the viridis color scale on the original CRS
Raster plot with ggplot2 using the viridis color scale on the original CRS

Plotting Tip

More information about the Viridis palette used above at R Viridis package documentation.

Plotting Tip

For faster, simpler plots, you can use the plot function from the terra package.

See ?plot for more arguments to customize the plot

R

plot(b10_casco_2023)

This map shows the sea surface temperature of our Casco Bay at one point in time in 2023. We can see that the maximum temperature is 80. While intuitively we know this is Farenheit (80C would be…. something), we don’t know for sure. We can look at the metadata of our object to see what the units are. Much of the metadata that we’re interested in is part of the CRS. We introduced the concept of a CRS in an earlier lesson.

Now we will see how features of the CRS appear in our data file and what meanings they have.

View Raster Coordinate Reference System (CRS) in R

We can view the CRS string associated with our R object using thecrs() function.

R

crs(b10_casco_2023, proj = TRUE)

OUTPUT

[1] "+proj=utm +zone=19 +datum=WGS84 +units=m +no_defs"

Challenge

What units are our data in?

+units=m tells us that our data is in meters.

Understanding CRS in Proj4 Format


The CRS for our data is given to us by R in proj4 format. Let’s break down the pieces of proj4 string. The string contains all of the individual CRS elements that R or another GIS might need. Each element is specified with a + sign, similar to how a .csv file is delimited or broken up by a ,. After each + we see the CRS element being defined. For example projection (proj=) and datum (datum=).

UTM Proj4 String

A projection string (like the one of b10_casco_2023) specifies the UTM projection as follows:

+proj=utm +zone=19 +datum=WGS84 +units=m +no_defs

  • proj=utm: the projection is UTM, UTM has several zones.
  • zone=19: the zone is 19
  • datum=WGS84: the datum is WGS84 (the datum refers to the 0,0 reference for the coordinate system used in the projection)
  • units=m: the units for the coordinates are in meters

Note that the zone is unique to the UTM projection. Not all CRSs will have a zone. Image source: Chrismurf at English Wikipedia, via Wikimedia Commons (CC-BY).

UTM zones in the USA.
The UTM zones across the continental United States. From: https://upload.wikimedia.org/wikipedia/commons/8/8d/Utm-zones-USA.svg

Calculate Raster Min and Max Values


It is useful to know the minimum or maximum values of a raster dataset. In this case, given we are working with temperature data, these values represent the min/max sea surface temperature range in Casco Bay.

Raster statistics are often calculated and embedded in a GeoTIFF for us. We can view these values:

R

minmax(b10_casco_2023)

OUTPUT

    SST_F_20230920
min       47.09686
max       80.46152

R

min(values(b10_casco_2023), na.rm = TRUE)

OUTPUT

[1] 47.09686

R

max(values(b10_casco_2023), na.rm = TRUE)

OUTPUT

[1] 80.46152

Data Tip - Set min and max values

If the minimum and maximum values haven’t already been calculated, we can calculate them using the setMinMax() function.

R

b10_casco_2023 <- setMinMax(b10_casco_2023)

We can see that the temperature at our site ranges from ~47F to ~80F.

Raster Bands


The Sea Surface Temperature object (b10_casco_2023) that we’ve been working with is a single band raster. This means that there is only one data set stored in the raster: SST at one time point.

Multi-band raster image

A raster dataset can contain one or more bands. We can use the rast() function to import one single band from a single or multi-band raster. We can view the number of bands in a raster using the nlyr() function.

R

nlyr(b10_casco_2023)

OUTPUT

[1] 1

However, raster data can also be multi-band, meaning that one raster file contains data for more than one variable or time period for each cell. By default the raster() function only imports the first band in a raster regardless of whether it has one or more bands. Jump to a later episode in this series for information on working with multi-band rasters: Work with Multi-band Rasters in R.

Bad Data Values in Rasters


Sometimes your rasters can have bad data values. These are different from NoData Values, which get represented by NAs. Bad data values are values that fall outside of the applicable range of a dataset.

Examples of Bad Data Values:

  • The normalized difference vegetation index (NDVI), which is a measure of greenness, has a valid range of -1 to 1. Any value outside of that range would be considered a “bad” or miscalculated value.
  • Reflectance data in an image will often range from 0-1 or 0-10,000 depending upon how the data are scaled. Thus a value greater than 1 or greater than 10,000 is likely caused by an error in either data collection or processing.
  • Coastal ocean data could be contaminated by measurements from land.

Find Bad Data Values

Sometimes a raster’s metadata will tell us the range of expected values for a raster. Values outside of this range are suspect and we need to consider that when we analyze the data. Sometimes, we need to use some common sense and scientific insight as we examine the data - just as we would for field data to identify questionable values.

Plotting data with appropriate highlighting can help reveal patterns in bad values and may suggest a solution. For example, let’s look at the range of our SST raster.

R

minmax(b10_casco_2023)

OUTPUT

    SST_F_20230920
min       47.09686
max       80.46152

47F seems reasonable, but 80? Maybe it is. But maybe it’s just land values that bled over. Let’s assume 75F is the real maximum. To view where we might have bad data, we can use classify() which takes a matrix with three columns. The first is a low value. The second is a high value. And the third is how we want that classified. Let’s say we wanted to look at bad values in our SST dataset.

R

# reclassify raster to ok/not ok
range_matrix <- matrix(c(
  40,75, 1, #low, high, make a 1
  75, 90, 2
), ncol = 3, byrow = TRUE)

b10_highvals <- classify(b10_casco_2023,
                         rcl = range_matrix)

plot(b10_highvals)
Raster plot showing location of extreme values
Raster plot showing location of extreme values

Yeah, it’s some spots at the tail-end of the coast that could indeed by pixels contaminated by land. To fix that, we can set values outside of our range to NA using clamp()

R

b10_casco_2023 <- clamp(b10_casco_2023, 
                        lower = 40,
                        upper = 75)

minmax(b10_casco_2023)

OUTPUT

    SST_F_20230920
min       47.09686
max       75.00000

Create A Histogram of Raster Values


We can explore the distribution of values contained within our raster using the geom_histogram() function which produces a histogram. Histograms are often useful in identifying outliers and bad data values in our raster data.

R

ggplot() +
    geom_histogram(data = b10_casco_2023_df, 
                   mapping = aes(x = SST_F_20230920))

OUTPUT

`stat_bin()` using `bins = 30`. Pick better value with `binwidth`.

Notice that a warning message is thrown when R creates the histogram.

stat_bin() using bins = 30. Pick better value with binwidth.

This warning is caused by a default setting in geom_histogram enforcing that there are 30 bins for the data. We can define the number of bins we want in the histogram by using the bins value in the geom_histogram() function.

R

ggplot() +
    geom_histogram(data = b10_casco_2023_df, 
                   mapping = aes(x = SST_F_20230920),
                   bins = 100)

Note that the shape of this histogram looks similar to the previous one that was created using the default of 30 bins. The distribution of SST values looks reasonable. Although, we can see some very thin tails that we might want to inspect to see if they are real values or bad data.

Challenge: Explore Raster Metadata

Use describe() to determine the following about the data/landsat_casco/b10_cropped/LC08_L2SP_011030_20130815_20200912_02_T1_ST_B10.TIF file:

  1. Does this file have the same CRS as b10_casco_2023_df?
  2. What is the NoData Value?
  3. What is resolution of the raster data?
  4. How large would a 5x5 pixel area be on the Earth’s surface?
  5. Is the file a multi- or single-band raster?

R

describe("data/landsat_casco/b10_cropped/LC08_L2SP_011030_20130815_20200912_02_T1_ST_B10.TIF")

OUTPUT

 [1] "Driver: GTiff/GeoTIFF"                                                                                                                                                                                                                                                                                                                          
 [2] "Files: data/landsat_casco/b10_cropped/LC08_L2SP_011030_20130815_20200912_02_T1_ST_B10.TIF"                                                                                                                                                                                                                                                      
 [3] "Size is 1128, 1349"                                                                                                                                                                                                                                                                                                                             
 [4] "Coordinate System is:"                                                                                                                                                                                                                                                                                                                          
 [5] "PROJCRS[\"WGS 84 / UTM zone 19N\","                                                                                                                                                                                                                                                                                                             
 [6] "    BASEGEOGCRS[\"WGS 84\","                                                                                                                                                                                                                                                                                                                    
 [7] "        DATUM[\"World Geodetic System 1984\","                                                                                                                                                                                                                                                                                                  
 [8] "            ELLIPSOID[\"WGS 84\",6378137,298.257223563,"                                                                                                                                                                                                                                                                                        
 [9] "                LENGTHUNIT[\"metre\",1]]],"                                                                                                                                                                                                                                                                                                     
[10] "        PRIMEM[\"Greenwich\",0,"                                                                                                                                                                                                                                                                                                                
[11] "            ANGLEUNIT[\"degree\",0.0174532925199433]],"                                                                                                                                                                                                                                                                                         
[12] "        ID[\"EPSG\",4326]],"                                                                                                                                                                                                                                                                                                                    
[13] "    CONVERSION[\"UTM zone 19N\","                                                                                                                                                                                                                                                                                                               
[14] "        METHOD[\"Transverse Mercator\","                                                                                                                                                                                                                                                                                                        
[15] "            ID[\"EPSG\",9807]],"                                                                                                                                                                                                                                                                                                                
[16] "        PARAMETER[\"Latitude of natural origin\",0,"                                                                                                                                                                                                                                                                                            
[17] "            ANGLEUNIT[\"degree\",0.0174532925199433],"                                                                                                                                                                                                                                                                                          
[18] "            ID[\"EPSG\",8801]],"                                                                                                                                                                                                                                                                                                                
[19] "        PARAMETER[\"Longitude of natural origin\",-69,"                                                                                                                                                                                                                                                                                         
[20] "            ANGLEUNIT[\"degree\",0.0174532925199433],"                                                                                                                                                                                                                                                                                          
[21] "            ID[\"EPSG\",8802]],"                                                                                                                                                                                                                                                                                                                
[22] "        PARAMETER[\"Scale factor at natural origin\",0.9996,"                                                                                                                                                                                                                                                                                   
[23] "            SCALEUNIT[\"unity\",1],"                                                                                                                                                                                                                                                                                                            
[24] "            ID[\"EPSG\",8805]],"                                                                                                                                                                                                                                                                                                                
[25] "        PARAMETER[\"False easting\",500000,"                                                                                                                                                                                                                                                                                                    
[26] "            LENGTHUNIT[\"metre\",1],"                                                                                                                                                                                                                                                                                                           
[27] "            ID[\"EPSG\",8806]],"                                                                                                                                                                                                                                                                                                                
[28] "        PARAMETER[\"False northing\",0,"                                                                                                                                                                                                                                                                                                        
[29] "            LENGTHUNIT[\"metre\",1],"                                                                                                                                                                                                                                                                                                           
[30] "            ID[\"EPSG\",8807]]],"                                                                                                                                                                                                                                                                                                               
[31] "    CS[Cartesian,2],"                                                                                                                                                                                                                                                                                                                           
[32] "        AXIS[\"(E)\",east,"                                                                                                                                                                                                                                                                                                                     
[33] "            ORDER[1],"                                                                                                                                                                                                                                                                                                                          
[34] "            LENGTHUNIT[\"metre\",1]],"                                                                                                                                                                                                                                                                                                          
[35] "        AXIS[\"(N)\",north,"                                                                                                                                                                                                                                                                                                                    
[36] "            ORDER[2],"                                                                                                                                                                                                                                                                                                                          
[37] "            LENGTHUNIT[\"metre\",1]],"                                                                                                                                                                                                                                                                                                          
[38] "    USAGE["                                                                                                                                                                                                                                                                                                                                     
[39] "        SCOPE[\"Engineering survey, topographic mapping.\"],"                                                                                                                                                                                                                                                                                   
[40] "        AREA[\"Between 72°W and 66°W, northern hemisphere between equator and 84°N, onshore and offshore. Aruba. Bahamas. Brazil. Canada - New Brunswick (NB); Labrador; Nunavut; Nova Scotia (NS); Quebec. Colombia. Dominican Republic. Greenland. Netherlands Antilles. Puerto Rico. Turks and Caicos Islands. United States. Venezuela.\"],"
[41] "        BBOX[0,-72,84,-66]],"                                                                                                                                                                                                                                                                                                                   
[42] "    ID[\"EPSG\",32619]]"                                                                                                                                                                                                                                                                                                                        
[43] "Data axis to CRS axis mapping: 1,2"                                                                                                                                                                                                                                                                                                             
[44] "Origin = (398865.000000000000000,4866405.000000000000000)"                                                                                                                                                                                                                                                                                      
[45] "Pixel Size = (30.000000000000000,-30.000000000000000)"                                                                                                                                                                                                                                                                                          
[46] "Metadata:"                                                                                                                                                                                                                                                                                                                                      
[47] "  AREA_OR_POINT=Area"                                                                                                                                                                                                                                                                                                                           
[48] "Image Structure Metadata:"                                                                                                                                                                                                                                                                                                                      
[49] "  COMPRESSION=LZW"                                                                                                                                                                                                                                                                                                                              
[50] "  INTERLEAVE=BAND"                                                                                                                                                                                                                                                                                                                              
[51] "Corner Coordinates:"                                                                                                                                                                                                                                                                                                                            
[52] "Upper Left  (  398865.000, 4866405.000) ( 70d15'36.90\"W, 43d56'37.75\"N)"                                                                                                                                                                                                                                                                      
[53] "Lower Left  (  398865.000, 4825935.000) ( 70d15' 9.45\"W, 43d34'46.27\"N)"                                                                                                                                                                                                                                                                      
[54] "Upper Right (  432705.000, 4866405.000) ( 69d50'19.04\"W, 43d56'51.69\"N)"                                                                                                                                                                                                                                                                      
[55] "Lower Right (  432705.000, 4825935.000) ( 69d50' 0.77\"W, 43d35' 0.04\"N)"                                                                                                                                                                                                                                                                      
[56] "Center      (  415785.000, 4846170.000) ( 70d 2'46.52\"W, 43d45'49.65\"N)"                                                                                                                                                                                                                                                                      
[57] "Band 1 Block=1128x1 Type=Float32, ColorInterp=Gray"                                                                                                                                                                                                                                                                                             
[58] "  Description = SST_F_20130815"                                                                                                                                                                                                                                                                                                                 
[59] "  Min=51.010 Max=89.659 "                                                                                                                                                                                                                                                                                                                       
[60] "  Minimum=51.010, Maximum=89.659, Mean=-9999.000, StdDev=-9999.000"                                                                                                                                                                                                                                                                             
[61] "  NoData Value=nan"                                                                                                                                                                                                                                                                                                                             
[62] "  Metadata:"                                                                                                                                                                                                                                                                                                                                    
[63] "    STATISTICS_MAXIMUM=89.659408569336"                                                                                                                                                                                                                                                                                                         
[64] "    STATISTICS_MEAN=-9999"                                                                                                                                                                                                                                                                                                                      
[65] "    STATISTICS_MINIMUM=51.00980758667"                                                                                                                                                                                                                                                                                                          
[66] "    STATISTICS_STDDEV=-9999"                                                                                                                                                                                                                                                                                                                    
  1. If this file has the same CRS as DSM_HARV? Yes: UTM Zone 19, WGS84, meters.
  2. What format NoData Values take? 0
  3. The resolution of the raster data? 1x1
  4. How large a 5x5 pixel area would be? 5mx5m How? We are given resolution of 1x1 and units in meters, therefore resolution of 5x5 means 5x5m.
  5. Is the file a multi- or single-band raster? Single.

Key Points

  • The GeoTIFF file format includes metadata about the raster data.
  • To plot raster data with the ggplot2 package, we need to convert it to a dataframe.
  • R stores CRS information in the Proj4 format.
  • Be careful when dealing with missing or bad data values.