Timeline for Calculate minimum area where x% of raster value total is concentrated within polygons
Current License: CC BY-SA 3.0
9 events
| when toggle format | what | by | license | comment | |
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| May 18, 2015 at 21:09 | comment | added | Dan | @ChrisW Sorry, I wasn't clear about that. It doesn't have to be contiguous, I just need the value. | |
| May 18, 2015 at 21:07 | comment | added | Chris W | @Lyngbakr Are you looking for an enclosed/contiguous region within the polygon or just a value when you talk about finding the smallest area of concentration? This answer and comments (and your response to Aaron above) seem to indicate just a value, not necessarily contiguous, which would considerably simplify the problem. | |
| May 18, 2015 at 17:32 | comment | added | Adrian | Also this on an old ESRI thread: forums.esri.com/Thread.asp?c=93&f=995&t=276826 | |
| May 18, 2015 at 17:30 | comment | added | Adrian | I just found a plug-in for QGIS called "RasterPixelCountStat" that will calculate the breaks for you - appears that's all it does so you'd still need create a Processing model or similar to use the value it generates | |
| May 18, 2015 at 17:17 | comment | added | Adrian | I'm not familiar with ArcGIS so can't comment but thinking about how it might be possible in QGIS (I've not had time to try it), I wonder if it may be possible to use the Processing toolbox in QGIS to create a model using an R script to calculate the 80/20 quartile boundary with the raster library eg. quantile(myraster, probs = c(0.20), type=7,names = FALSE). This would give you the 80/20 boundary as an input to the QGIS Raster/Extract/Contours tool to generate a contour line around the area. Equally you could use the raster calculator to set any value less than the generated value to 0. | |
| May 18, 2015 at 17:10 | comment | added | Dan | I think your general approach is right, though. Perhaps the following workflow: 1) find the 20th percentile for each polygon, 2) mask the data below that value, 3) sum the area covered by the remaining data. | |
| May 18, 2015 at 17:05 | comment | added | Adrian | I'm not familiar with ArcGIS so can't comment, and I've been trying to find a tidy way to do it in QGIS and so far haven't found one. | |
| May 18, 2015 at 16:46 | comment | added | Dan | How would I go about doing that? | |
| May 16, 2015 at 9:09 | history | answered | Adrian | CC BY-SA 3.0 |