Feature request #9124

Heatmap in percentage

Added by Paolo Cavallini over 10 years ago. Updated over 6 years ago.

Category:Analysis library
Pull Request or Patch supplied:No Resolution:invalid
Easy fix?:No Copied to github as #:17761


Heatmaps would be far more convenient (easier to interpret in many contexts) if they could (optionally) be expressed in % rather than in absolute values (in inverse values, so one could create isolines including, say, 95% probability). The change seems trivial:

  • calculate the maximum
  • dividing the raster values by that
  • adding an option to choose between absolute values and %

Also a note on the help on how to interpret cell values would make life easier for newbies.


#1 Updated by Nyall Dawson over 10 years ago

It's actually not quite that simple - the maximum value is not known until the entire heatmap is generated, it can't be calculated in advance.

The actual process would be:
1. Generate the heatmap
2. Scan for the max and min values within the heatmap (The minimum value would also need to be considered, since points could potentially have a negative weighting set resulting in raster values < 0)
3. Update the cell values with a value relative to the max/min values

I'm wondering if it would be better/more flexible for this to be done via a step in a processing script. Problem is that heatmaps can't be generated via scripts at the moment - this would require moving the heatmap code from a c++ plugin to core (something which should be done at some time in any case). This is on my (distant) radar, alongside adding additional hotspot types such as Getis Ord Gi*. I'm hoping to get funding or some time of sponsorship to tackle this.

#2 Updated by Jürgen Fischer over 10 years ago

  • Subject changed from Heathmap in percentage to Heatmap in percentage

#3 Updated by Matthias Kuhn over 10 years ago

Alternative for moving to core:
We could add the possibility to expose a python API from C++ plugins as well. I could provide some code I have written for globe which does exactly this.

#4 Updated by Jürgen Fischer almost 10 years ago

  • Category changed from C++ Plugins to 114

#5 Updated by Giovanni Manghi over 7 years ago

  • Category changed from 114 to Analysis library

#6 Updated by Giovanni Manghi over 7 years ago

  • Target version set to Version 3.0

#7 Updated by Giovanni Manghi about 7 years ago

  • Easy fix? set to No

#8 Updated by Paolo Cavallini over 6 years ago

  • Description updated (diff)

Still true in QGIS 3

#9 Updated by Nyall Dawson over 6 years ago

  • Status changed from Open to Feedback

I think this should be closed, and replaced with a feature request for a processing algorithm which scales raster values to percent of max.

Heatmaps are part of processing now, so only the scaling algorithm is missing from this request.

#10 Updated by Paolo Cavallini over 6 years ago

  • Resolution set to invalid
  • Status changed from Feedback to Rejected

Fully agreed.

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