gdal_merge.py support?

[cody-elhard]

Is there any workarounds to get gdal_merge.py to work or do we need to manually install gdal with python support?

From the docs. gdal_merge.py is a Python script, and will only work if GDAL was built with Python support.

https://gdal.org/programs/gdal_merge.html

[edmorley]

Hi!

This buildpack is maintained on a best effort basis only. It's not used at all within Heroku, so we generally don't really understand much about how GDAL works.

I presume from your wording that something isn't working (it's implied but not explicitly stated; including an error message in cases like this is helpful)?

If there is a configure option or similar that needs to be adding to the GDAL builds, then I'd accept a PR: https://github.com/heroku/heroku-geo-buildpack/blob/79e30b559963daa796fe8f6ca0c82457e0677851/builds/gdal/gdal.sh#L16

[cody-elhard]

I will need to investigate this a bit.

There is a subset of gdal utilities that are built with Python. https://gdal.org/user/gdal_python_utilities.html I believe Python is part of the base Heroku stack.

In our instance I get

$ python --version
Python 3.10.12

[cody-elhard]

@edmorley thanks for the timely response.

So looking at the flags for configure it appears we can pass a --with-python flag.

It appears python is included on every stack meaning this should pass?

We don't have access to AWS_ACCESS_KEY_ID so we can't test this ourselves.

➜  gdal-3.5.0 ./configure --help
`configure' configures this package to adapt to many kinds of systems.

Usage: ./configure [OPTION]... [VAR=VALUE]...

...

Optional Packages:
  ...
  --with-python=ARG   Enable python bindings (ARG=yes, no, or path to python binary)

[edmorley]

Ah so it seems that the GDAL project now has Debian packages available: https://gdal.org/download.html#debian

It may be possible to use those via https://github.com/heroku/heroku-buildpack-apt rather than needing this buildpack. Longer term that seems a more sustainable option than us trying to keep this buildpack going.

[edmorley]

So I looked into this as part of #53.

Enabling the Python bindings during the build of the GDAL library for this buildpack wouldn't be ideal, since:

• it would link against system Python, which (a) would probably cause issues for apps also using the Python buildpack (which is most of the consumers using this buildpack), (b) doesn't exist in the run image for Heroku-24.
• would require some manual site-packages or PYTHON_PATH tricks to try and get the Python packages generated by the build to be found at runtime

However, I found that the GDAL Python package from PyPI already includes gdal_merge.py, so this feature was actually already supported by using that package.

ie:

1. Add this buildpack and the Python buildpack to your app
2. Add GDAL to requirements.txt so the Python buildpack installs the GDAL Python package too
3. Use via the command gdal_merge.py (the GDAL package configures it as a console script during package installation)

eg:

$ heroku run bash
Running bash on ⬢ emorley-geo-test... up, run.1550 (Basic)
~ $ cat requirements.txt | tail -n1
GDAL
~ $ gdal_merge.py --help
Usage: gdal_merge.py [--help] [--help-general]
                     [-o <out_filename>] [-of <out_format>] [-co <NAME>=<VALUE>]...
                     [-ps <pixelsize_x> <pixelsize_y>] [-tap] [-separate] [-q] [-v] [-pct]
                     [-ul_lr <ulx> <uly> <lrx> <lry>] [-init "<value>[ <value>]..."]
                     [-n <nodata_value>] [-a_nodata <output_nodata_value>]
                     [-ot <datatype>] [-createonly] <input_file> [<input_file>]...
                     [--help-general]