Hi all I want to write a raster calculator and have two problems with Python and GDAL.
My first problem: when calculating a difference between two raster bands I get a wrong results. Raster in ERDAS IMAGINE format (HFA) and bands extracted correctly. When I print each band and subtraction result I get something similar to this BAND 1 [[ 118 121 121 ..., 111 108 107]....]] BAND 5 [[ 156 162 159 ..., 148 145 142]....]] DIFFERENCE [[218 215 218 ..., 219 219 221]....]] But when calculate difference between two separate TIFFs (each band in separate file) - result is ok RASTER 1 [[ 118. 121. 121. ..., 111. 108. 107.]....]] RASTER 5 [[ 156. 162. 159. ..., 148. 145. 142.]....]] DIFFERENCE [[-38. -41. -38. ..., -37. -37. -35.]....]] Here is my code and sample files http://www.4shared.com/file/212381308/a3e3f140/gdal_numpytar.html. Run examples as: - bands subtraction: test_bands.py landsat-6bands/s1986-06-12-163.img - files subtraction: test_files.py landsat-separate-files/band1.tif landsat-separate-files/band5.tif Can anyone help? What is wrong in my code? Second problem: processing large rasters. I get error File "C:/Documents and Settings/alex/.qgis//python/plugins\rastercalc\rastercalcutils.py", line 162, in layerAsArray array = gdalData.ReadAsArray() File "C:\OSGeo4W\apps\gdal-16\pymod\osgeo\gdal.py", line 603, in ReadAsArray return gdalnumeric.DatasetReadAsArray( self, xoff, yoff, xsize, ysize ) File "C:\OSGeo4W\apps\gdal-16\pymod\osgeo\gdal_array.py", line 108, in DatasetReadAsArray return numpy.concatenate( array_list ) MemoryError Large rasters is landsats with 6 bands, 30m/pixel, scene size is aprox. 185x185 km, aprox. 9000x9000 pixels. On disk one file occupied ~500-700 Mb. Some files can be larger, up to 15000x15000 pix. and more. Is it possible to work with large files? Maybe it is possible to process small pieces of this files and then merge this pieces into one large file? Where I can found more information about this? Thanks P.S.: sorry for my English, I'm Ukrainian -- Alexander Bruy alexander.b...@gmail.com _______________________________________________ gdal-dev mailing list gdal-dev@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/gdal-dev
