[mapserver-dev] RFC-108 : heatmap generation

[thomas bonfort]

Hi Even,
I haven't looked at the gdal implementation, but from what you explain
I guess that we're not doing the processing steps in the same order.
The proposed implementation first accumulates all the vector samples
in a 1 band float pixmap, and then applies a gaussian filter on this
pixmap. As such, the number of sample points does not influence the
processing time (aside from the initial accumulation, but that step
has a linear computation time wrt the number of features, that can't
be cut down). I haven't investigated the final difference between the
two methods; if the gdal one is more rigorous it might be added as an
alternate method should the need arise.

--
Thomas

On 30 January 2014 21:25, Even Rouault <even.rouault at mines-paris.org> wrote:
> Le jeudi 30 janvier 2014 17:58:07, Thomas Bonfort a écrit :
>> 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.
>
> Hi Thomas,
>
> Very cool. As it somehow related to what gdal_grid does (admitedly in a less
> beautiful fashion), I'm wondering if you've thought about the performance
> implications of a point layer with a lot of features (I've not looked at your
> code). Iterating over each point for each pixel might be very slowly. For some
> modes of gdal_grid I had started building a in-memory quadtree to speed-up the
> search for candidate points. Or perhaps you assume that the point layer has a
> spatial index (PostGIS, .qix, etc...) and use msQueryByRect() ?
>
> Even
>
>>
>> best regards,
>> thomas
>>
>> [1] http://mapserver.org/development/rfc/ms-rfc-108.html
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