error with gdalbuildvrt, in Python

Question

I am new to python/GDAL and am running into perhaps a trivial issue. This may stem from the fact that I don't really understand how to use GDAL properly in python, or something careless, but even though I think I am following the help doc, I keep getting a syntax error when trying to use "gdalbuildvrt".

What I want to do is take several (amount varies for each set, call it N) geotagged 1-band binary rasters [all values are either 0 or 1] of different sizes (each raster in the set overlaps for the most part though), and "stack" them on top of each other so that they are aligned properly according to their coordinate information. I want this "stack" simply so I can sum the values and produce a 'total' tiff that has an extent to match the exclusive extent (meaning not just the overlap region) of all the original rasters. The resulting tiff would have values ranging from 0 to N, to represent the total number of "hits" the pixel in that location received over the course of the N rasters.

I was led to gdalbuildvrt [http://www.gdal.org/gdalbuildvrt.html] and after reading about it, it seemed that by using the keyword -separate, I would be able to achieve what I need. However, each time I try to run my program, I get a syntax error. The following shows two of the several different ways I tried calling gdalbuildvrt:

gdalbuildvrt -separate -input_file_list stack.vrt inputlist.txt
gdalbuildvrt -separate stack.vrt inclassfiles

Where inputlist.txt is a text file with a path to the tif on every line, just like the help doc specifies. And inclassfiles is a python list of the pathnames. Every single time, no matter which way I call it, I get a syntax error on the first word after the keywords (i.e. 'inputlist' in inputlist.txt, or 'stack' in stack.vrt).

Could someone please shed some light on what I might be doing wrong? Alternatively, does anyone know how else I could use python to get what I need?

Thanks so much.

Answer 1

gdalbuildvrt is a GDAL command line utility. From your example its a bit unclear how you actually run it, but when running from within Python you should execute it as a subprocess.

And in your first line you have the .vrt and the .txt in the wrong order. The textfile containing the files should follow directly after the -input_file_list.

From within Python you can call gdalbuildvrt like:

import os
os.system('gdalbuildvrt -separate -input_file_list inputlist.txt stack.vrt')

Note that the command is provided as a string. Using a Python list with the files can be done with something like:

os.system('gdalbuildvrt -separate stack.vrt %s') % ' '.join(data)

The ' '.join(data) part converts the list to a string with a space between the items.

Depending on how your GDAL is build, its sometimes possible to use wildcards as well:

os.system('gdalbuildvrt -separate stack.vrt *.tif')