On Fri, 1 Jul 2022, Ainslie Johnstone wrote:
Hi there,
I am trying to downsample a high-resolution file of gridded
population estimates (1km res over the whole world). I want the
downsampled version to give the total population in the new
lower-resolution grid. However, whenever I downsample using gdalwarp
-r sum, I don’t seem to be getting this. Instead the new values in
the lower-resolution grid (no matter what resolution it is) seem to
be more like the max, rather than the sum, of the old
high-resolution grid. If I add up the total population across the
whole grid it is far lower than it should be. How much lower depends
on how much I have downsampled.
I am making sure to exclude the no data values, and have tried a
whole variety of different output resolutions and projections. Any
suggestions as to why this might be?
1. Are your working type -wt and output type -ot big enough to store
the population of the new pixels ?
2. If you don't need to record nodata, you could *try* making the
nodata value 0 and treat them as data.
--
Andrew C. Aitchison Kendal, UK
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