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v.rast.stats: note about vector overlap limitation #1730

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Jan 13, 2022
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v.rast.stats: note about vector overlap limitation #1730

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vector overlap limitation
jfbourdon Jul 16, 2021
a56ad09
v.rast.stats: use topological terminology in manual
metzm Jan 12, 2022
4a7ba15
v.rast.stats: example for areas with multiple cats
metzm Jan 13, 2022
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Expand Up @@ -31,6 +31,16 @@ <h2>NOTES</h2>
will be chopped off.
<p>If a MASK is present, it will be restored after the script finished.
The script changes temporarily to the resolution of the given raster map.
<p>If an area has several categories in the selected layer (equivalent
to overlapping polygons in Simple Features), only one category will be
kept during the rasterization process. Statistics for the skipped
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Shouldn't skipped there be replaced by kept? The skipped will be skipped, no? So the resulting stats for kept categories will be partial.

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In the case of two polygons partially overlapping, you have three topological areas where one area has two categories, shared with the other two areas:

  • area 1: category 1
  • area 2: category 2
  • area 3: categories 1, 2

Let's assume, for area 3 category 1 has been used: statistics for category 1 are complete and for category 2 incomplete because category 2 has been skipped for area 3. Thus resulting stats for skipped categories are partial.

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Thanks for clarification, Markus. I re-created the plot in a paper here. So, you mean it's partial because category 2 will be considered only in area 2 in this case then?

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I have added a more detailed explanation. OK, @veroandreo?

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Yes, thanks Markus :)

categories will thus be partial.
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<p>
For example, if there are three areas: area 1 with cat 1, area 2 with
cat 2, area 3 with cats 1, 2. Only one category value of area 3 will be
used for rasterization, the other category value will be skipped. Thus
statistics for the used category value will be complete, while
statistics for the skipped category value will be incomplete.
<p><!-- r.univar limitation -->
Large amounts of system memory can be used when extended statistics
(<em>first_quartile,median,third_quartile,percentile </em>) are being requested
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