How do I change the pixel size in GDAL without changing the extent?

Question

I need to change the pixel size of a GTiff in Gdal without changing the extent.

When I use gdal_translate -tr xres yres src_dataset dst_dataset

It changes the extent. I do not need a rescaling or interpolation. I just need to change the pixel size value from .041 to 4.6 for both x and y and not change anything else including the extent. Think of it as changing a value in the header.

OR

the inverse.

Just overwrite the extent but not change the pixel size would work. Open to Arc solutions as well.

Answer 1

Here's a quick script I put together to correct the cell size of a folder of GeoTiff rasters:

import os, sys

from osgeo import gdal
from osgeo import gdalconst

WorkingFolder = sys.argv[1] # first command line argument
# change to a hard path like r'c:\your\path' or 'c:\\your\\path'
# without the r if it suits your purposes..

for f in os.listdir(WorkingFolder):   # loop through for each file in the folder
    fName, fExt = os.path.splitext(f) # break up file name and extension
    if fExt.upper() == '.TIF':
        # this is a tif file, open it and get the existing geotransform
        ds = gdal.OpenShared(os.path.join(WorkingFolder,f),gdalconst.GA_Update) # open the raster using FULL path
        gt = ds.GetGeoTransform()
        # gt is a tuple :
        # adfGeoTransform[0] /* top left x */
        # adfGeoTransform[1] /* w-e pixel resolution */
        # adfGeoTransform[2] /* 0 */
        # adfGeoTransform[3] /* top left y */
        # adfGeoTransform[4] /* 0 */
        # adfGeoTransform[5] /* n-s pixel resolution (negative value) */
        # from http://www.gdal.org/gdal_tutorial.html

        # you only want to change 1 and 5 but tuples are read-only so
        # I convert to a list:
        gtLst = list(gt)

        # change the pixel size here
        # 'y' pixel size is usually negative
        gtLst[1] = 4.6
        gtLst[5] = -4.6

        # apply the changes
        ds.SetGeoTransform(gtLst)
        ds = None # close the dataset and commit the changes

It's mostly comments but shows the key points. The updated cell size is hard coded, perhaps it should be a variable, but will work in this case.

Be careful of GeoTIFF with world files - this will only update the TIFF and not the TFW file (unless the TIF is not a GeoTIFF) which will lead to contradictions in georeference, depending on what other packages do with this situation you could still end up with the old cell size. It's best to remove any TFW files that exist (move to another folder just in case the georeference isn't embedded).