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

[Rahkonen Jukka (Tike)]

Thomas Bonfort wrote:

> Hi Jukka,
> Thanks for the comments, which I mostly agree with. I should clearly
> remove references to the the term of "interpolation" as it does not
> apply to the proposed solution. Concerning the "heatmap" term that
> should be replaced by "kernel density" that could be a possibility,
> although as you said the "heatmap" term has become so common that I'd
> suspect many users wouldn't give a "kernel density" solution a look even
> if that is what they are after.
> I'll rework the RFC to suppress the interpolation references, and use a
> "connectiontype density", would that work for you?

Everybody calls them as heatmaps so let it be so but make a difference between density and interpolation. Connectiontype interpolation can be reserved for the future.

>> I am not sure if this image generator can even make such heatmaps like the salinity map in the beginning of RFC where missing data between the measuring points are (linearly?) interpolated. In that map the density of salinity measurement stations has no effect on the colour. Also in real life even if you measure a hundred times a temperature of +40 degrees from very close measuring points, the maximum temperature does not rise a bit over +40.
> correct, the proposed solution will be biased by samples close to one
> another.

>> The system itself is welcome and I am interested in seeing how the problem of creating automatically a good looking visualization for changing map scales is solved. Perhaps output pixel based interpolation radius and PROCESSING “NORMALIZATION=AUTO" will handle that.
> I'm not sure I understand what you're looking for here, can you be a bit
> more precise?

I tried to say that same settings for radius and colorrange tend to work well only for a limited scale range. Here are two examples which are using the same traffic accidend data.
http://www.hs.fi/kotimaa/Nettisivusto+paljastaa+Helsingin+vaarallisimmat+risteykset/a1305551700052
This one overrates accidents at small scale and burns everything red. When you zoom in the accidents almost disappear and the hotspots are lost.
http://cloudnsci.fi/wiki/demos/traffic_accidents_in_Helsinki_heatmap.html
This one is static and looks good at medium scales but does not work well at big and small scales.

I feel that the search radius and colorrange should be adjusted somehow by the scale but I can't suggest how. But perhaps it can be done rather easily with a few scale dependent classes.

-Jukka Rahkonen-



--
thomas

>
> -Jukka Rahkonen-
>
> ________________________________________
> Thomas Bonfort wrote:
>
>> Devs,
>
>> please have a look at RFC-108 [1]. The associated code and the RFC are
>> still beta, so there's still plenty of room for modification or remarks.
>
>> best regards,
> thomas
>
> [1] http://mapserver.org/development/rfc/ms-rfc-108.html
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