[Gdal-dev] export an image to ascii text file

[Bryan Keith]

Xiaodong,

Attached is a python script that I've used to do part of what you've 
asked for (I'm pretty sure this list accepts attachments).  It's not a 
polished tool, but the code may help you get started.

Note that the xy calculations are dependent on the cell size being the 
same in x and y.  You'll notice that this will only output a single band 
as it's currently written.  Also it doesn't attempt to project to lat 
and lon.  It outputs the coordinates of the images projection.

Even with these caveats maybe it helps.

Bryan

Bryan Keith
GIS Specialist
Geomega, Inc.
Boulder, CO, USA

Xiaodong Zhang wrote:

> Hi,
>
> I need to export an image (any projection) into an ascii file: coma 
> delimited columns of lat, lon, band 1, band 2, ..... Before I get on 
> that with GDAL library, does anyone have developed or know of such a 
> program, which can be shared.
>
> Thanks
> Xiaodong
>
-------------- next part --------------
import gdal, sys, struct
from gdalconst import *
def Usage():
	print "Usage: RasterToXYZ.py rastername rasterband outputasciifile"
	print "This routine will write out ascii XYZ data for the input raster."
	print "rasterband is typically 1 (the first band)"
	return
if len(sys.argv) != 4:
	Usage()
	sys.exit()
dataset = gdal.Open(sys.argv[1],GA_ReadOnly)
band = dataset.GetRasterBand(int(sys.argv[2]))
geotransform = dataset.GetGeoTransform()
#geotransform[0],geotransform[3] are the (x,y) of the upper left corner of the upper left
#pixel
#geotransform[1] is the cell size in x
#geotransform[5] is the cell size in y (in this case cell size is the same in x and y)
#the following line reads a row (constant y) of data (the top most (ymax) row)
#scanline = band.ReadRaster(0,0,band.XSize,1,band.XSize,1,GDT_Float32)
#tuple_of_floats = struct.unpack('f' * band.XSize, scanline)
#the following line reads the second row of data
#scanline = band.ReadRaster(0,1,band.XSize,1,band.XSize,1,GDT_Float32)
f = open(sys.argv[3],'w')
f.write('x,y,z\n')
for y in range(band.YSize): #from 0 to 838
  scanline = band.ReadRaster(0,y,band.XSize,1,band.XSize,1)
  tuple_of_floats = struct.unpack('f' * band.XSize, scanline)
  x = 0
  strY = str((geotransform[3] - (geotransform[1] * 0.5)) - (y * geotransform[1]))
  for z in tuple_of_floats:
    f.write(str((x * geotransform[1]) + geotransform[0] + (geotransform[1] * 0.5)) + ",")
    f.write(strY + ",")
    f.write(str(z) + '\n')
    x = x + 1
f.close()