Hi Ari,

Interesting result. It looks roughly right: pixels with only dark points in 
their surrounding window are dark and pixels with only light point in the 
window are light.

However, it does seem that the legend used for pixels uses different interval 
values than that for the pixels. Otherwise it would be hard to explain why 
pixels that have only a single point in their window do not have the same color 
as that point.

The second thing that is concerning is the ragged edge of the apparent circles. 
It suggests that the distance calculation is not accurate. It shouldn't be more 
than a pixel off.

You will always have these awkward edge effects in moving window analysis. 
However it can be reduced by 1) using a window radius considerably larger than 
the distance between points. 2) use a distance weighted kernel (my weapon of 

Kind regards, Alex
From: gdal-dev <gdal-dev-boun...@lists.osgeo.org> on behalf of Ari Jolma 
Sent: Saturday, March 10, 2018 10:00:00 AM
To: gdal-dev@lists.osgeo.org
Subject: [gdal-dev] Wondering gdal_grid moving average interpolation

I'm translating things on QGIS and now looking at GDAL tool rasterizing
point data set with moving average interpolation.

That's making a call to gdal_grid with -a average.

I've got the attached result from a point set (circles with red border
and inside inverse grayscale with interpolated value). The call was

gdal_grid -l INPUT -zfield suuntap -a
-ot Float32 -of GTiff INPUT.shp OUTPUT.tif

I'm wondering is that the expected since it looks like the raster cell
value is determined by point locations. I would have expected a much
more smooth surface without any obvious circular shapes. To me it looks
like the computation was not done cell by cell but instead point by point.

What am I missing or misunderstanding?


ps: This tool is in group 'Raster analysis'. In my opinion it should be
in a group 'Point data tools' or something.

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