Hi all,
I’m trying to mask a band from a GeoTiff file like so:
>>> from osgeo import gdal, ogr, osr
>>> from gdalconst import *
>>> import numpy as np
>>> import matplotlib as mpl
>>> dataset = gdal.Open('001.tif')
>>> band = dataset.GetRasterBand(1)
>>> ba = band.ReadAsArray()
>>> print "Origin:", ba[0, 0], type(ba[0, 0]) # NODATA value in image == zero
Origin: 0 <type 'numpy.uint16'>
>>> print "(5, 5):", ba[5, 5], type(ba[5, 5])
(5, 5): 42271 <type 'numpy.uint16'>
>>> print "Nodata:", band.GetNoDataValue() # NODATA from file == None
Nodata: None
>>> print "Mask flags:", band.GetMaskFlags()
Mask flags: 1
>>> band.SetNoDataValue(0) # Set the NODATA value to zero
>>> print "Nodata:", band.GetNoDataValue(), type(band.GetNoDataValue())
Nodata: 0.0 <type 'float’>
>>> mb = band.GetMaskBand()
>>> ma = mb.ReadAsArray()
>>> print "Origin:", ma[0, 0], type(ma[0, 0]) # *** SHOULD BE ZERO!!! ***
Origin: 255 <type 'numpy.uint8'>
>>> print "(5, 5):", ma[5, 5], type(ma[5, 5]) # Correct
(5, 5): 255 <type 'numpy.uint8'>
>>> print np.any(ma==0) # Mask band is entirely 255
False
As you can see, the mask covers the entire image and not the zeros on the edge.
The band.GetNoDataValue() is returning a Python float() which leads me to
suspect that there is incorrect type handling within GDAL’s Python wrapping
such that the mask generation is trying to compare the band’s raster values
(GDAL_UInt16) to whatever the NoDataValue type is stored internally. Am I way
off base or is there something I’m missing?
Cheers!
______________________________________________
Dave Welch Software Engineer
URTHECAST
111 West Port Plaza Suite 300 l St. Louis, MO l USA l 63146
urthecast.com<http://www.urthecast.com/> l Connect
@urthecast<https://twitter.com/urthecast>
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