Actually the Heatmap process *does* allow specifying an attribute of the
input geometries to be used as a weighting attribute (parameter
"weightAttr" - see
http://suite.opengeo.org/opengeo-docs/cartography/rt/heatmap.html). So
maybe you have what you need already!
This still doesn't address the original problem, because:
- the output range of the Heatmap is in [0,1], rather than the units of the
input attribute (and there's no obvious way of correlating the two, AFAIK)
- since Heatmap is a density surface, the maximum value at any single point
is less than the original input value at that point. Barnes surface also
does a certain amount of averaging, but the effect is much less.
There's a good explanation by whuber of the difference between heatmaps and
interpolation surfaces in one of the comments of the gis.stackexchange
post. Incidentally, after reading whuber's complaint about the misuse of
the term "Heatmap" I sort of wish I'd called the process KernelDensity
instead...
M
On Tue, Jan 8, 2013 at 1:44 PM, Rahkonen Jukka <jukka.rahko...@mmmtike.fi>wrote:
> Hi,
>
> There are also use cases for density maps weighted by a value of some
> attribute like sum of dollars lost in traffic accidents. Barnes surfaces
> does not suit for this, nor unweighted density maps. I have been creating
> such visualisations with SAGA GIS and Sextante which both have functions
> for this but the result is a static image that does not suit well for a web
> map with large scale range.
> Discussion about this and one nice image in
> http://gis.stackexchange.com/questions/39074/whats-the-best-way-to-produce-a-density-map-from-weighted-points-in-qgis
>
> It would be nice to be able to do something similar dynamically with
> Geoserver.
>
> -Jukka Rahkonen-
>
> ________________________________
> Martin Davis wrote:
>
> +1 for everything Andrea said about Heatmaps - they are density maps, not
> interpolation surfaces.
>
> Also, the output values are in the range [0,1], which is another reason
> you saw only one color in your output.
>
> On Tue, Jan 8, 2013 at 6:17 AM, Andrea Aime <andrea.a...@geo-solutions.it
> <mailto:andrea.a...@geo-solutions.it>> wrote:
> On Tue, Jan 8, 2013 at 3:14 PM, Chris Haste <cha...@airdata.co.uk<mailto:
> cha...@airdata.co.uk>> wrote:
> Hi Andrea,
>
> I’m not sure I understand. Are you saying that I don’t have a sufficient
> number of points in my data? I have a regular grid of points covering the
> entire globe at 1.25 x 1.25 degree intervals. Is this not dense enough?
>
> I'm saying a heatmap shows a color based on the different concentration of
> points, not their value, so if the grid is regular it's normal that
> you get a solid color.
>
> If you want to interpolate a value contained in the attributes of the
> points instead you have to use the Barnes surface instead.
> See some docs here:
> http://suite.opengeo.org/docs/cartography/rt/barnes.html
>
> Cheers
> Andrea
>
>
> From: andrea.a...@gmail.com<mailto:andrea.a...@gmail.com> [mailto:
> andrea.a...@gmail.com<mailto:andrea.a...@gmail.com>] On Behalf Of Andrea
> Aime
> Sent: 08 January 2013 14:09
> To: Chris Haste
> Cc: geoserver-users@lists.sourceforge.net<mailto:
> geoserver-users@lists.sourceforge.net>
> Subject: Re: [Geoserver-users] gs:Heatmap problems
>
> On Tue, Jan 8, 2013 at 3:03 PM, Chris Haste <cha...@airdata.co.uk<mailto:
> cha...@airdata.co.uk>> wrote:
> Hi List,
>
> I have been trying to use the new heatmap transformation in version 2.2.3
> but I think I must be doing something wrong.
> I wish to display a layer defined using an SQL view. The query simply
> returns a Grid of points and for each point there is a temperature value, I
> am using the round function in the query to round the temperature value to
> the nearest integer.
>
> I am using the SLD below, copied from the example and modified to
> (hopefully) work with my data. However, the entire map is produced in one
> colour (#FFFF00) but when I query the map by clicking on it in an
> Openlayers preview it shows correct values for the Temperatures and
> different locations on the map yield different values.
>
> Any ideas?
>
> Heatmaps are about point density, if you want to interpolation function
> you should look at the Barnes surface transformation
> instead
>
> Cheers
> Andrea
>
>
> --
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