I have an integer raster for which I would like to build a raster attribute table using Python and GDAL. I can create a GDAL raster attribute table in Python as follows:
>>> rat = gdal.RasterAttributeTable()
This works fine, as we can see:
>>> rat <osgeo.gdal.RasterAttributeTable; proxy of <Swig Object of type 'GDALRasterAttributeTableShadow *' at 0x0000000002A53D50> >
The table thus created has no rows or columns:
>>> rat.GetRowCount() 0 >>> rat.GetColumnCount() 0
I create a column called "Value" to store the unique values in the raster:
>>> rat.CreateColumn("Value", gdalconst.GFT_Integer, gdalconst.GFU_MinMax) 0
This is fine, and the column count is updated:
>>> rat.GetColumnCount() 1
Now I have to add values (records) to the column for it to be of any use. I can get a list of unique values from the raster's band like so:
>>> data = band.ReadAsArray(0, 0, dataset.RasterXSize, dataset.RasterYSize) >>> vals = list(numpy.unique(data)) >>> vals [3, 7, 8, 10, 11, 12, 13, 14, 17, 18, 20, 22, 23, 25, 27, 28, 41, 45, 52, 56]
What I would like to do is create a for loop to loop through
vals and populate the column in the attribute table. I thought I could do something like this:
>>> for i in range(len(vals)): rat.SetValueAsInt(i, 0, vals[i])
i is the row (record),
0 is the field index and
vals[i] is the integer value I want to insert. But it causes an error:
Traceback (most recent call last): File "<pyshell#32>", line 2, in <module> rat.SetValueAsInt(i, 0, vals[i]) File "C:\Python27\lib\site-packages\osgeo\gdal.py", line 1139, in SetValueAsInt return _gdal.RasterAttributeTable_SetValueAsInt(self, *args) TypeError: in method 'RasterAttributeTable_SetValueAsInt', argument 4 of type 'int'
The error is caused because I use
vals[i] in the call to
SetValueAsInt() rather than using an integer directly. For example,
rat.SetValueAsInt(0, 0, 0) works fine, but is useless for populating the column if I just want to loop over the list of unique values.
Is this a known issue? Google has so far not been very useful. What can I do to get around this problem?