[Gdal-dev] C# Bindings

[Simon Perkins]

Hi,

Michael Paul and Morten Nielson posted some hand-rolled C# bindings to 
this list a few weeks back. I've reworked and extended that effort to 
produce a partial set of C# bindings for GDAL that are very similar to 
the C++ classes that underlie GDAL, i.e. we have C# classes for 
Gdal.Dataset, Gdal.RasterBand, and so forth. Underneath it all, it calls 
the GDAL C API, using the C# Pinvoke mechanism (which in turn calls the 
GDAL C++ classes!). The bindings are written for C# 2.0 and use modern 
features like generics, so you'll need Visual Studio 2005 to get these 
to work.

Attached is a VS 2005 solution with two projects: the GDAL bindings 
library, and a simple windows test application that allows you to load 
in and view an image via GDAL. To see it in action, unpack the solution, 
make sure you have the GDAL library in a directory pointed to by your 
PATH variable, build and run the test application. I used the FWTools 
distribution in which the GDAL library is called gdal_fw.dll, so if you 
want to use a GDAL that's named differently, e.g. gdal13.dll, then 
change the library name defined as the gdalDll constant at the top of 
InterOp.cs.

To use the GDAL bindings in your own code, you can do things like:

string myFile = "testfile.tif";
using (Gdal.Dataset dataset = new Gdal.Dataset(myFile)) {
    // Get the width, height and number of bands
    int width = dataset.XSize;
    int height = dataset.YSize;
    int nBands = dataset.RasterCount;
    // Get the projection string
    string projection = dataset.GetProjection();
    // Get the GDAL driver for this format
    Gdal.Driver driver = dataset.GetDriver();
    // Get the format name
    string format = driver.LongName;
    // Read the first band of the image into a byte array
    Gdal.RasterBand band = dataset.GetRasterBand(1);
    byte[] buffer = new byte[width * height];
    band.RasterIO(Gdal.RWFlag.Read, 0, 0, width, height, buffer, width, 
height);
}  // Dataset is automatically closed at this point


Note that just like the GDALDataset C++ class, a Gdal.Dataset must be 
associated with a file upon construction and will automatically 
open/create that file. You can close the file either by explicitly 
calling Close(), or by making use of the using() { .. } construct as 
above. This makes sure that Dispose() is invoked on the Dataset as soon 
as the Dataset goes out of scope, which in turn just invokes Close().

The raw Pinvoke bindings are all contained in the file InterOp.cs, so in 
theory, this could be generated entirely by SWIG. Unfortunately I know 
nothing about SWIG and so far I haven't been able to get SWIG to 
successfully compile bindings with Visual Studio 2005. It's actually 
pretty straightforward to add  new Pinvoke signatures to InterOp.cs by 
hand, though getting SWIG to take care of that would be nice. Any input 
on that appreciated! I'm assuming that SWIG isn't going to be able to 
generate the C# class-oriented interface, but I don't know enough about 
it to be sure.

This partial implementation is good enough for my needs now. If anyone 
else wants to use it, please feel free. If you want to extend it and 
send updates to me, great! The code doesn't contain any explcit licence 
headers, but Michael was suggesting an MIT licence, same as GDAL. Fine 
with me.

Cheers,

Sy

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