[gdal-dev] python: setting nodata affects all bands

[Matt Wilkie]

Hi Folks,

I'm endeavouring to teach myself a little about pythin and gdal by 
working on a python script to set the nodata value on a raster. I've 
encountered a puzzling thing and I don't know if this is expected 
behaviour or I'm doing something wrong. If set nodata on a single band, 
all of the bands are affected. For my current project this doesn't 
matter, but it just doesn't seem right to me.

In the script below I expected band 1 to be changed and the others to 
remain as they are.

----- gdalsetnull.py -----
import gdal
import sys
import os.path

if len(sys.argv) < 2:
	 print "Usage: gdalsetnull.py raster_file null_value"
	 sys.exit(1)

input = sys.argv[1]
null_value = sys.argv[2]

dataset = gdal.Open( input, gdal.GA_Update )
if dataset is None:
     print 'Unable to open', input, 'for writing'
     sys.exit(1)

b1 = dataset.GetRasterBand(1)
b2 = dataset.GetRasterBand(2)
b3 = dataset.GetRasterBand(3)

print 'Initial nodata:\t', b1.GetNoDataValue(), b2.GetNoDataValue(), 
b3.GetNoDataValue()

b1.SetNoDataValue( float(null_value) )

print 'Output nodata:\t', b1.GetNoDataValue(), b2.GetNoDataValue(), 
b3.GetNoDataValue()
---------------------------

I'm using GDAL 1.5.0b1, FWTools 2.0.3, released 2007/12/10


-- 
matt wilkie
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