C# & Mapscript - Setting Environment Variables At Runtime

Question

I am working on an application that makes use of the c# Mapscript bindings. When I manually set and/or append to the GDAL_DATA, GDAL_DRIVER_PATH, PROJ_LIB, and PATH environment variables - the application code works beautifully.

For a number of reasons, I am trying to avoid permanently setting/changing these environment variables. I am under the impression that by using the .NET frameworks Environment.SetEnvironmentVariable method, that I should be able to set these environment variables at runtime for the current process.

This approach seems to work in some capacity - as the mapscript objects initialize properly (i.e., I dont get PInvoke errors...etc). In my code snippet below, I get an error at map.draw() complaining about GDAL_DATA and gcs.csv.

// add some new environment vars
// TODO check if they may already exist - in which case append to
Environment.SetEnvironmentVariable("GDAL_DATA",MY_GDAL_DATA_PATH)
Environment.SetEnvironmentVariable("GDAL_DRIVER_PATH",MY_GDAL_DRIVER_PATH)
Environment.SetEnvironmentVariable("PROJ_LIB",MY_PROJ_LIB_PATH)

// append to existing PATH variable
string pathVariable = Environment.GetEnvironmentVariable("PATH")
pathVariable += MY_PATH_VARS
Environment.SetEnvironmentVariable("PATH",MY_PATH_VARS)

mapObj map = new mapObj(transmitterMapFile);
map.setSize(request.Width, request.Height);
map.setExtent(extent[0], extent[1], extent[2], extent[3]);

imageObj img = map.draw();

Does anyone see something wrong with this approach? Or is there a better way to set these variables at runtime?

Answer 1

I use a similar approach in Python with MapScript on Windows and it works fine.

Careful with the following code:

pathVariable += MY_PATH_VARS
Environment.SetEnvironmentVariable("PATH", MY_PATH_VARS)

I believe it should be:

pathVariable += MY_PATH_VARS
Environment.SetEnvironmentVariable("PATH", pathVariable)

I'd look at the C# sourcecode for GdalGoneWild - "Using GDAL in .NET without a big headache"

The environment variable setup code should be of particular interest. The author also mentions in an associated blog post:

One little strange thing I noticed was that I was not able to set up the GDAL_DATA environment variable programmatically. So instead I used Gdal.SetConfigOption which overrides the environment variable.

A couple of final things to check. Are you registering the GDAL drivers elsewhere in your code?

Gdal.AllRegister();

Finally the PATH must contain semi-colons between each specified path.

C:\dir1;C:\dir2