[gdal-dev] Correct way to create a new GTiff, with numpy.zeros() and python bindings

[Dane Springmeyer]

Hi list,

Im just starting to use the python bindings and have been  
experimenting with gdal_rasterize which great results, effectively  
burning in multiple different colors based on some related vector  
shapefile attributes.  The trick to getting started was that I did not  
have any raster (at the right extent and resolution) to copy from, so  
to get started I followed the api tutorial to create and new Gtiff.

This code works perfectly for my usecase:

from osgeo import gdal
from osgeo import osr
import numpy

driver = gdal.GetDriverByName('GTiff')
dst_ds = driver.Create( "/Users/spring/projects/wind/data/processed/ 
wpc_final.tif", 7850, 3500, 4, gdal.GDT_Byte)
dst_ds.SetGeoTransform( [-124.75, .001, 0.0, 49.02, 0.0, -.001] )
srs = osr.SpatialReference()
srs.ImportFromEPSG(4326)
dst_ds.SetProjection( srs.ExportToWkt() )


But the tutorial also has the step of writing zeros over the image  
with numpy. Since I am already burning in the required values into my  
raster with gdal_rasterize this seems not to matter, but I am really  
curious for future uses how to get this step working. Starting with  
zeros, or any default value would be useful.

So, if I execute the following code block next:

zeros = numpy.zeros( (7850, 3500) )
dst_ds.GetRasterBand(1).WriteArray( zeros )
dst_ds.GetRasterBand(2).WriteArray( zeros )
dst_ds.GetRasterBand(3).WriteArray( zeros )
dst_ds.GetRasterBand(4).WriteArray( zeros )


I get the error:
'ValueError: array larger than output file, or offset off edge'  which  
obviously means that I am writing the wrong size numpy array into my  
raster.

So, what do I need to know to figure out the right dimensions for the  
numpy.zeros() function? Some slick fraction of my image size in pixels  
and my geotransform?

Thanks,

Dane

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