Geospatial Computing from the Command Line

Installation

This commands on this page uses gdal and jq. On Ubuntu these can be installed using:

sudo apt install gdal-bin jq

Get information about a raster

gdalinfo provides information about raster files.

gdalinfo myraster.tif will produce a basic readable output to the screen.

This output can also be written to JSON

gdalinfo -json myraster.tif

Writing to JSON makes it easy to use individual pieces, e.g., to look up the dimensions of the raster (you’ll need to install jq to do this).

gdalinfo -json myraster.tif | jq -r .size

or just the width of the raster

gdalinfo -json myraster.tif | jq -r .size[0]

Splitting rasters using gdal

One way to split a raster into pieces is to use the gdal_retile.py Python script bundled with gdal.

The following command will split myraster.tif into 1500x1500 pixel rasters stored in outputdir. The first number is the width (in pixels) and the second is the height (in pixels) of each chunk.

gdal_retile.py -ps 1500 1500 -targetDir outputdir myraster.tif

Files will be labeled with _row_col and so if the original image was 4500x1500 then the above command would produce three output files:

myraster_1_1.tif
myraster_2_1.tif
myraster_3_1.tif

Representing the top of the original raster (_1_1), the middle of the original raster (_2_1), and the bottom of the original raster (_3_1).

Split raster into horizontal strips

Our most common usage is to split large rasters into horizontal strips with manageable file sizes (< 3 GB). This can be automated by changing myraster.tif to the location of your raster and outputdir to the directory you want the split raster pieces stored in and running the code below:

RASTER=myraster.tif
OUTPUTDIR=outputdir
WIDTH=$(gdalinfo -json $RASTER | jq -r .size[0])
WIDTHPAD=$((WIDTH + 10)) # Padding prevents periodic inclusion of single pixel strip 
HEIGHT=$(expr 1000000000 / $WIDTH)
gdal_retile.py -ps $WIDTHPAD $HEIGHT -targetDir $OUTPUTDIR $RASTER

Combining/merging rasters using gdal

One way to combine rasters is to use the gdal_merge.py Python script bundled with gdal. We use LZW compression to reduce file sizes while ensuring that the resulting GeoTIFF can be used in all geospatial computing systems.

gdal_merge.py -co COMPRESS=LZW -o output_file.tif input_file_1.tif input_file_2.tif input_file_3.tif