[gdal_contour] Do not include min/max when polygonize #11673
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Fixes OSGeo#11564 by not including raster min/max when polygonize and fixed levels are specified. MIN and MAX literals can be used to specify raster min/max values, e.g.: -fl MIN 10 20 30 MAX
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| This would create 10-meter polygonal contours from the DEM data in :file:`test.asc` and produce a GeoJSON output | ||
| with the contour min and max elevations in the ``min`` and ``max`` attributes, the values of these fields will | ||
| be: (4.0, 10.0), (10, 15.0), (15, 20.0) and (20, 36.0). | ||
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Shoud it be (10, 15.0), (15, 20.0) and (20, 30.0)?
I think I understand what happens, but not how to describe it so that a newcomer understands. Perhaps something like
"Creates contours at regular 10 meter intervals and adds extra contour for a fixed 15 m level. Finally turns areas between the contours into polygons."
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For those values, shouldn't user define -i 10 -fl MIN 15 MAX -p? Otherwise it would not match with the title. Or do regular intervals start/stop at min/max automatically? It does make sense, most users want to get the polygon between the sea and 10 m level automatically, but it is not clear from the documentation.
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Maybe a bit different approach would have been easier to explain. First improve documentation of -p
"Generate contour polygons rather than contour lines. The min and max values of the raster will be used as the lower and upper limit for the data range of the first and last polygon, respectively.
Then introduce exlude_min and exclude_max for preventing the default behavior so that it would have similar effect on all -i and -fl combinations, when used together with -p, and no effect without -p.
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For those values, shouldn't user define
-i 10 -fl MIN 15 MAX -p? Otherwise it would not match with the title. Or do regular intervals start/stop at min/max automatically? It does make sense, most users want to get the polygon between the sea and 10 m level automatically, but it is not clear from the documentation.
yes, regular intervals get min/max automatically. I didn't change that.
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| The minimum and maximum values from the raster are not automatically added to | ||
| the fixed levels list but the special values `MIN`` and `MAX`` (case insensitive) | ||
| can be used to include them. | ||
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... but when option -i is used together with -p, the minimum and maximum values from the raster ARE automatically added, and there is no way to get rid of them.
I know this is not a common use case, but there can be lot of writing to the -fl if the DEM has a large height range.
| This would create 10-meter polygonal contours from the DEM data in :file:`test.asc` | ||
| and produce a GeoJSON output with the contour min and max elevations in the ``min`` | ||
| and ``max`` attributes, not including the minimum and maximum values from the raster. | ||
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I do not understand. If there is only -i, doesn't it mean, that min/max are used just like before the change?
Or maybe I just need another cup of coffee.
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You a re right: I removed the not.
Fixes #11564 by not including raster min/max when polygonize and fixed levels are specified.
MIN and MAX literals can be used to specify raster min/max values, e.g.:
-fl MIN 10 20 30 MAX