Some Processing I’ve Done in GDAL

I have GDAL installed in Linux (i.e. the easiest way to install/implement it) so the following examples represent command line usage. I have used a smattering of different GDAL utilities, and the links in the descriptions go to the manual page for the utility in each example. I have incorporated these example commands into various bash scripts if I need to implement them in an iteration over multiple files.

This is an example of re-sampling a raster to larger pixel sizes (in this case to a lower resolution of 0.09 degree from the original 0.0002 degree [30m LANDSAT pixels]) by taking the mean of the pixels encompassed in the coarser output.

gdalwarp -tr 0.09 0.09 -r average -ot Float32 file.tif fileout.tif
This is the output of the above command, where a 30m resolution image was scaled up to 10km resolution image. The new pixel values are the averages of the binary raster pixels (0,1) that contributed to them. All maps are plotted in R 3.4.1

I have used GDAL to set no data values (in this case, I reclassified 0 as the no data value).

gdal_translate -of GTiff -a_nodata 0 PPR/2000/Playas_2000.tif region_img/Playas.tif

Here’s an example of stitching 2 tiff’s together into a larger area, and setting the output no data value to be where the 0’s were in the original input files. -o region_img/Canada.tif -a_nodata 0 PPR/2000/Alberta_PPR_2000.tif PPR/2000/SAK_MAN_PPR_2000.tif
Notice blue is the only color, representing the only value left in the raster (1).

If you want to stitch shape files together into a new file, you have to initialize the new shape file first with one of your input files and then add to it.

ogr2ogr regions/Canada.shp shapefiles/Alberta_PPR_2001.shp
ogr2ogr -update -append regions/Canada.shp shapefiles/SAK_MAN_PPR_2001.shp -nln Canada

If you’re going to, say, turn your raster into polygons, you can get rid of clumps below a certain threshold before doing so (in this case, I’m getting rid of single pixels in my unary raster when using an 8-neighbor clumping rule). -st 2 -8 file.tif

Then, I can make my polygon layer, simplified. In the 2nd line, I project the shapefile to Albers Equal Area. -8 file.tif -f "ESRI Shapefile" shapefile/file.shp 
ogr2ogr -f "ESRI Shapefile" -progress outfile.shp shapefile/file.shp -t_srs "EPSG:5070"
Here’s a shape file of wetlands created from the TIFF of the Canadian Prairie Pothole Region!

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