1,219 reputation
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location South Africa
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visits member for 2 years, 2 months
seen Jul 18 at 12:11

Apr
19
revised How to rename field names in a shapefile from the commandline?
fields -> field names
Apr
19
asked How to rename field names in a shapefile from the commandline?
Apr
19
answered How to rename field names in a shapefile from the commandline?
Apr
16
awarded  Caucus
Mar
28
comment Getting Transparent Circles with Heatmap Plugin
Here's a useful explanation of why it's not recommended to do analysis in Pseudo Mercator (also known as Web Mercator): blogs.esri.com/esri/arcgis/2010/03/05/… If you are only after the "heatmap effect" and not worried about the spatial meaning (x points within kernel radius), then you can get away with generating heatmaps with data in EPSG:3857 projection. If those numbers are important, then it's best to reproject.
Mar
28
comment Getting Transparent Circles with Heatmap Plugin
I'm glad you got it working! I usually do it this way: 1) load the points as WGS84, 2) save that layer in a UTM projection (if the area fits within one UTM zone, otherwise some appropriate local projection). 3) create the heatmap using the projected points as input 4) reproject resulting heatmap to pseudo mercator using raster warp 5) load openlayers. You shouldn't have any alignment problems that way, and you're not doing analysis in pseudo mercator (which can lead to distortion errors).
Mar
26
answered How to use ZonalStats plugin?
Mar
26
comment How to use QGIS Zonal Stats Plugin from Python Console?
@vinayan the QProgressDialog is useful for visual environments where you want to see how far the calculations have progressed. It has no use from the command line. You can use None as the parameter and it works fine. Then you don't need the from PyQt4.. line or the progressDialog = line. See similar post at gis.stackexchange.com/questions/23203/…
Mar
26
comment How to calculate raster statistics for polygons?
Thanks for your comment, Dan. My answer was missing a necessary import statement, which should now be fixed.
Mar
26
revised How to calculate raster statistics for polygons?
added import statement
Mar
26
awarded  Necromancer
Mar
26
awarded  Nice Question
Mar
26
comment Heatmap algorithm to visualise point diversity
Come to think of it, that wouldn't be a problem if you added each new heatmap to the composite heatmap after each category. The question is then which approach would be computationally faster to implement - raster sums or pixel-by-pixel calculation.
Mar
26
comment Heatmap algorithm to visualise point diversity
I have added a visualisation to my question based on this suggestion, and the result looks good! The disadvantage is that if you're dealing with hundreds or thousands of categories, storing all of those rasters is going to be a problem.
Mar
26
revised Heatmap algorithm to visualise point diversity
added normalised sum visualisation
Mar
26
comment How to select by polygon in PostGIS with misaligned layers?
Your query finished in 10 min, while my buffer query is still running 11 hours later. I have visually checked the result, and could find no false positives or false negatives. I did find a few areas where the selected polygons extended beyond the biome edge, and these were selected correctly (buffering would not select these). So at least based on my data, this is the way that works!
Mar
26
accepted How to select by polygon in PostGIS with misaligned layers?
Mar
26
revised How to select by polygon in PostGIS with misaligned layers?
query takes substantially longer than the hour initiallly indicated
Mar
25
comment How to select by polygon in PostGIS with misaligned layers?
What a cunning idea! Computationally it's much better, but I imagine it might be prone to false positives? I have a polygon count for your method, but I'm still waiting for my buffer to finish! I'll test more tomorrow.
Mar
25
revised Heatmap algorithm to visualise point diversity
added caveat for binning strategy