Dear all,

I'm sorry if this is a too basic question, but I'm trying to make a
overlay() of spatial polygon with a srtm ASCII altitude map. I tried to read
this map using readasciigrid, but it is to big for the computer's memory.
The only way that I find to read this map  is use GDAL.open, but doesn't
seems to have a method to do overlay with GDALReadOnlyDataset. There is some
way to use overlay or something like it,with this kind of data, or another
way to make overlay() with big grids?

Thanks,
Jorge

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