[gdal-dev] gdal_contour: min value unexpected

[Paul Meems]

Hi List,

I tried my command on GDAL 3.8.4, released 2024/02/08.
And the results are the same. The lowest value is still incorrect.

I can't imagine this is a bug that was never noticed before.
So I assume I'm doing something wrong. But I can't figure it out.

Please give me some advice.

Regards,

Paul

Op vr 5 apr 2024 om 10:27 schreef Paul Meems <bontepaarden at gmail.com>:

> Hello List,
>
> I have a Surfer grid which I want to convert into polygons using
> gdal_contour.
> The min value of the lowest polygon is 0 which I didn't expect.
> In the next step, I calculate the average of the min and max values, and
> in this case that average is wrong.
>
> These are the values of the grid:
> Grid Size (X*Y):       113 x 121
> NoData Value:          1.70141E+38
> Minimum:               105000
> Maximum:               133000
>
> This is my command:
> gdal_contour -p -f "ESRI Shapefile" -fl -97000 -37000 23000 83000 89000
> 95000 101000 107000 113650 121000 129000 137000 143000 149000 155000 215000
> 275000 335000 -amin Min -amax Max "Surfer.grd" "tmp3p4f4i.shp"
>
> As you can see, the lowest value of the grid (105000) is between the
> values 101000 and 107000.
> So I would expect to have the min value of the shapefile be 101000 and the
> max value 107000.
>
> But the result is:
> [image: image.png]
> Min is 0 and max is 107000.
>
> I also tried setting the lowest value of the grid to 107000 (one of the
> level values) but that also resulted in a min value of 0.
>
> The polygons themselves are OK, just the min value of the lowest value is
> incorrect.
>
> I'm using GDAL 3.6.3, released 2023/03/07 on Windows.
>
> Why is this happening?
> Do I need to set an additional argument?
>
> Please advise.
>
> With regards,
>
> Paul
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/gdal-dev/attachments/20240419/4261554a/attachment-0001.htm>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image.png
Type: image/png
Size: 5407 bytes
Desc: not available
URL: <http://lists.osgeo.org/pipermail/gdal-dev/attachments/20240419/4261554a/attachment-0001.png>