Heatmap in percentage

[qgib]

Author Name: Paolo Cavallini (@pcav)
Original Redmine Issue: 9124

Redmine category:analysis_library

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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.

[qgib]

Author Name: Nyall Dawson (@nyalldawson)

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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.

[qgib]

Author Name: Jürgen Fischer (@jef-n)

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• subject was changed from Heathmap in percentage to Heatmap in percentage

[qgib]

Author Name: Matthias Kuhn (@m-kuhn)

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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.

[qgib]

Author Name: Jürgen Fischer (@jef-n)

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• category_id was changed from C++ Plugins to 114

[qgib]

Author Name: Giovanni Manghi (@gioman)

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• category_id was changed from 114 to Analysis library

[qgib]

Author Name: Giovanni Manghi (@gioman)

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• fixed_version_id was configured as Version 3.0

[qgib]

Author Name: Giovanni Manghi (@gioman)

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• easy_fix was configured as 0

[qgib]

Author Name: Paolo Cavallini (@pcav)

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Still true in QGIS 3

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• description was changed from 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. to 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.

[qgib]

Author Name: Nyall Dawson (@nyalldawson)

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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.

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• status_id was changed from Open to Feedback

[qgib]

Author Name: Paolo Cavallini (@pcav)

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Fully agreed.

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• resolution was changed from to invalid
• status_id was changed from Feedback to Rejected