Extract points within a shape from a raster
You need a library that can read your raster. I am not sure how to do that in Python but you could look at geotools (especially with some of the new raster library integration) if you want to program in Java. If you are good with C I would reccomend using something like GDAL.
If you want to look at a desktop tool you could look at extending QGIS with python to do the operation above.
If I remember correctly, the Raster extension to PostGIS may support clipping rasters based upon vectors. This means you would need to create your circles to features in the DB and then import your raster but then you might be able to use SQL to extract your values.
If you are really just a text file with numbers in a grid then I would go with the suggestions above.
I have a raster file (basically 2D array) with close to a million points. I am trying to extract a circle from the raster (and all the points that lie within the circle). Using ArcGIS is exceedingly slow for this. Can anyone suggest any image processing library that is both easy to learn and powerful and quick enough for something like this?
Thanks!