How to Resample GeoTIFF on Python?

Question

I am trying to resample a GeoTIFF file from pixels representing 30m² to pixels representing 1000m² on Python.

I have a geotiff that has the data according to those coordinates. The spatial resolution is 30m². I would like to change that to 1000m².

I was originally able to do this on QGIS while projecting (warping) the CRS from W84 to EPSG 7390. However, I would like to do the resampling without changing the CRS. When I tried it on QGIS I got an error ("creating 0x0 dataset).

I tried doing it on Python using GDAL but ran into the same error. Here is the code I used (from this Stack Exchange post:

from osgeo import gdal

infn = '/path/to/source.tif'
outfn = '/path/to/target.tif'

xres=1000
yres=1000
resample_alg = 'near'

ds = gdal.Warp(outfn, infn, xRes=xres, yRes=yres, resampleAlg=resample_alg)
ds = None

This is the GDAL error:

ERROR 1: Attempt to create 0x0 dataset is illegal,sizes must be larger than zero.

Also, just to check that the problem wasn't in opening the files, I also ran:

referenceFile = infn
reference = gdal.Open(referenceFile, 0)  # this opens the file in only reading mode
referenceTrans = reference.GetGeoTransform()

To which the output was:

(-58.168519761062974, 0.0002694945852358564, 0.0, -17.16626609035358, 0.0, -0.0002694945852358564)

I'm not entirely sure what I'm doing wrong here. I am very new to geographical data and would really appreciate some help. How do I

Note: I wasn't sure whether to post this here or on StackExchange, so please let me know if it doesn't belong here.

Please clarify your specific problem or provide additional details to highlight exactly what you need. As it's currently written, it's hard to tell exactly what you're asking. — Community
– Community Bot, Commented May 3, 2023 at 20:32

Rutger Kassies · Accepted Answer · 2023-05-04 08:16:37Z

0

You need to provide the resolution in the unit of the output projection. So if you don't change it, and the projection is EPSG:4326 (WGS84), the units are degrees. So you are asking GDAL to warp to a resolution of 1000 degrees, which as the error shows results in an invalid output dimension of 0x0 pixels.

A resolution of 1000 meters is more or less ~0.009 degrees (1km / 111km per degree latitude). There isn't a 1-on-1 mapping between resolution in meters and degrees, because it depends on the location itself. You can see the table in the link below for some examples:
https://en.wikipedia.org/wiki/Longitude#Length_of_a_degree_of_longitude

So using 0.009° as the resolution should be closer to what you expect, but the exact resolution you need might depend on the actual application.

edited May 4, 2023 at 8:16

answered May 4, 2023 at 6:49

Rutger Kassies

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