[mapserver-users] Heatmap / choropleth from points attributes

[Puneet Kishor]

On Wed, Feb 23, 2011 at 04:28:31PM +0100, Milo van der Linden wrote:
> Turning points into polygons (or voronois) is the "thinking like a GIS
> professional" approach. This is valid, but not as good as it can get.
> Basically, using imaging techniques would be a better approach.

Very well put.

> 
> Perhaps you can take this: http://www.sethoscope.net/heatmap/ as a starting
> point? The author has created a nice python script to generate a heatmap.

And here is a Perl-based approach
[http://blog.imtrevor.com/2009/07/16/generating-heat-maps-using-perl/]


> 
> 2011/2/23 Josh Jordan <outerspaceman81 at yahoo.com>
> 
> > First, you have to turn your points into shapes, theres some algorithm that
> > will turn points into polygons with borders midway between each point.
> >  Then, you have to add classes to the mapfile.  Add one class per color.
> >  You have to calculate the bounds and color for each class like this:
> >
> > CLASS
> >     EXPRESSION(([POPULATION] gt 90457) AND ([POPULATION] le 108397))
> >     STYLE
> >       COLOR 10 20 50
> >     END
> > END
> >
> > If your CSV data isnt joined to the mapserver data, you have to calculate
> > what shapes are in each bucket like this-
> >
> > CLASS
> >     EXPRESSION(([NAME] = "Shape1") OR ([NAME] = "Shape2"))
> >     STYLE
> >       COLOR 10 20 50
> >     END
> > END
> >
> > --- On *Tue, 2/22/11, Daniel Cole <daniel at southernsolutionsms.com>* wrote:
> >
> >
> > From: Daniel Cole <daniel at southernsolutionsms.com>
> > Subject: [mapserver-users] Heatmap / choropleth from points attributes
> > To: mapserver-users at lists.osgeo.org
> > Date: Tuesday, February 22, 2011, 10:06 PM
> >
> > I am a new mapserver user and have spent countless hours over the last
> > month reading, trying code, etc. before posting here for help.  I am trying
> > to generate an image (non-interactive) on a webpage based off of attribute
> > data in a points file.  For example, 20 different points equally distributed
> > in a field contain data about the moister level of the soil.  I want to make
> > the lowest levels blue and the highest levels yellow, or something like that
> > with some gradients in between.  If possible I want it to have interpolated
> > data between them to show the gradual change, but that isn't a must.   I
> > also want to wrap it in a polygon that trims the edges.
> >
> > I found some python code that I thought might do the trick , but it seems
> > lots of heat maps are based off of how many points exist in a certain area,
> > and thats now what I am doing.
> >
> > My points contain numbers in the attributes, 5, 25, 92, 71, etc.   I feel
> > like I am missing some easy way to do this right in front of me with gdal or
> > something.  If someone has any direction or even demo code that would be
> > greatly appreciated.
> >
> > Thanks,
> >
> > Daniel
> >
> > -----Inline Attachment Follows-----
> >
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