[gdal-dev] GDALSetGeoTransform, & using masks

[Patrick Cannon]

Hello Everyone,

I have what I hope to be just a couple of quick questions.

I am in the process of writting my own driver/dataset for BSB files so I can 
support version 4 and 5 files.  This way the code for handling these files 
is not in the standard GDAL library and should isolate it from Maptech.

I have run into a bit of a snag though.  Is it possible to create an affine 
transform matrix from the GCP values?  Or could I use Polynomial X to L, Y 
to L, L to X and L to Y values?

I have a class to handled the Polynomials and convert between Map to Pixel 
and Pixel to map but, I do not see a clean way of implementing this within 
the GDAL framework.

My next question has to do with masks.  For example, the chart image has a 
white border around it and I do not want it to show/count when asking the 
dataset to build the image.  This is further complicated by needing to use 
a polygon instead of a rectangle to describe the visible part of the image.

Is it possible to use a mask to hide the unwanted portion? 
Even if I am only reading part of the image?
Is there an example somewhere on how to do this?
Is there a better way to handle this?  

Thank you for any help or guidance you can provide.

Best regards,
Patrick Cannon