[mapserver-dev] [mapserver-users] RFC-108 : heatmap generation

Rahkonen Jukka (Tike) jukka.rahkonen at mmmtike.fi
Wed Feb 5 04:10:54 PST 2014

Thomas Bonfort wrote:
> The underlying problem I think is that heatmaps aren't designed to represent
> your data passed a given scale. We could however ease the task of generating
> consistent outputs by specifying the kernel radius in geographical units rather
> than in pixels. I'm a bit weary to implement that though, as it would be very easy
> to specify a radius that results in a huge raster buffer being allocated, and could
> easily lead to denials of service. Another shortcut that would avoid having to
> define multiple scale-dependant layers would be to use the RFC86 scaletoken
> mechanism to define multiple kernel radiuses and/or normalization values.

I have a third suggestion which is a variation of your second one. What affect the heatmap appearance are two factors, radius and weight which are both obviously numeric. Scale is numeric too, so perhaps the rest could be handled with mathematics?  You implement HM:RADIUS_FORMULA and HM:WEIGHT_FORMULA processing options and perhaps some clever people will discover what kind  of formulas will yield a nice smooth good looking transitions for all scales with only one single layer. Obviously Mapserver should pass the scale or scaledenominator as a variable so it could be utilized in the formula. HM stands for heatmap namespace and leaves field open for utilizing the same idea for other processes.

-Jukka Rahkonen-

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