[gdal-dev] python bindings

[Frank Warmerdam]

Robert Denham wrote:
> 
> Hi gdal-developers,
> can someone help me understand how to modify
> and
> create images using the gdal and gdalnumeric python modules?
> 
> I have no trouble reading the files in, but am a bit confused about how to
> save changes and close the image.
> 
> For example, under gdalnumeric, you can use:
> 
> from Numeric import *
> import gdalnumeric
> 
> array=gdalnumeric.LoadFile("/some/image.tiff")
> array2=array*-1

Robert,

The problem is that the raw arrays in numpy don't have information like
georeferencing or projections associated with them. The following script
demonstrates how to create a GDAL Dataset object associated with an array
and to assign the projection and georeferencing to it, and then write to an
output file. I hope it makes things clearer.

Best regards,

---------------------------------------+--------------------------------------
I set the clouds in motion - turn up | Frank Warmerdam, warmerdam at p...
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush | Geospatial Programmer for Rent

#!/usr/bin/env python

import gdal
import gdalnumeric

from Numeric import *

def SaveArrayWithGeo( array, src_filename, dst_filename, format='GTiff' ):

# Read information from source file.
src_ds = gdal.Open(src_filename)
gt = src_ds.GetGeoTransform()
pj = src_ds.GetProjection()
src_ds = None

# Create GDAL dataset for array, and set georeferencing.
src_ds = gdalnumeric.OpenArray( array )
src_ds.SetGeoTransform( gt )
src_ds.SetProjection( pj )

# Write array dataset to new file. 
driver = gdal.GetDriverByName( format )
if driver is None:
raise ValueError, "Can't find driver "+format

return driver.CreateCopy( dst_filename, src_ds )



if __name__ == '__main__':

filename = '/home/warmerda/openev/utm.tif'
array = gdalnumeric.LoadFile( filename )
array2 = 255 - array
array2 = array2.astype(Float32)
SaveArrayWithGeo( array2, filename, 'out.tif' )