Can't get gdal_merge Python script to run

Question

I downloaded and installed GDAL. I am using Python 27. I had to use the following commands at the IDLE Python GUI:

from osgeo import gdal,ogr
sys.path.append('C:\Program Files\GDAL')
import gdal_merge

I actually have C:\Program Files\GDAL listed first in my Path environmental system variables, so I don't know why I need to do the above. Anyway, when I try to use this utility, I don't get an error, but it only opens the Python script for editing, and doesn't run the script. I know that the documentation for gdal_merge states "NOTE: gdal_merge.py is a Python script, and will only work if GDAL was built with Python support." I did install GDAL with Python support, and can get some utilities to run correctly (like gdalwarp.exe) but have trouble running the python scripts.

How can I find out for sure if my installation of GDAL has Python support?

Answer 1

If you can do from osgeo import gdal,ogr your GDAL was built with the Python bindings otherwise you wouldn't be able to import it.

If you want to start a GDAL utility (gdalwarp, gdal_translate, gdal_merge) from within Python your best bet is to use Pythons subprocess module as these utilities are spawned from the command line.

An example:

import subprocess
merge_command = ["python", "gdal_merge.py", "-o", "output.tif", "input1.tif", "input2.tif", "input3.tif", "inputN.tif"]
subprocess.call(merge_command)

• Renee Cammarere: I didn't get an error message inside the Python Shell, but it doesn't appear to have done anything when I typed in: merge_command = ["python", "gdal_merge.py", "-o", "C:\output.tif", "C:\N31.DT1", "C:\N30.DT1"] A command window flashed when I typed in subprocess.call(merge_command) and then displayed a number 2, but didn't create the output file. Did I do something wrong? Thanks!
• Renee Cammarere: I know that any number other than a 0 returned from calling the merge command means that there was an error, but I don't know what it's having trouble with.

Answer 2

I think your problem is that the Python path and/or the GDAL paths are not set. If you do not need to run gdal_merge.py from a custom python script, you can run it from Windows Command line (cmd.exe):

Open the cmd.exe and insert the following line and you should get the usage of gdal_merge.py:

C:\Python27\python.exe C:\Python27\Scripts\gdal_merge.py

Maybe you have to adopt the paths to your Python Installation.

Answer 3

Or you can use %%bash. Something like that:

%%bash
gdal_merge.py -separate -of HFA -co COMPRESSED=YES -o output.img input1.TIF input2.TIF