Re: [OpenMap Users] Density layer or hotspot layer function in openmap?

From: Don Dietrick <>
Date: Thu, 15 Feb 2007 11:05:55 -0500

Hi Jeroen,

You can create a density surface several different ways in OpenMap,
but it comes down to having your layer display the information in an
OMRaster (OMRaster, OMScalingRaster) object, or an OMGrid object. It
depends on what your source data looks like and how you access that
data. To use an OMRaster, you would create a
java.awt.image.BufferedImage and render directly into it based on
your data, and then pass that BufferedImage to an OMRaster for
positioning. That would force you to manage the representation of
the data in the image.

The OMGrid is really build for representing grid data, though. You
use a GridData object to hold your data values, and the OMGrid object
holds the GridData and the position information about the GridData.
The OMGrid also uses an OMGridGenerator object to interpret the
GridData and create other OMGraphics to render to the map. The
OMGridGenerator is really where your focus will be, because that's
what decides how your data will be visualized. The
com.bbn.openmap.omGraphics.grid package contains a bunch of
OMGridGenerator implementations, the simplest one being a
SimpleColorGenerator that interprets the grid data as color values.

I'd start with a Layer that extends OMGraphicHandlerLayer and
overrides the prepare() method to return an OMGraphicList with an
OMGrid on it. Use the prepare method from the DemoLayer as an
example of mananging the OMGraphicList for a layer, and how to create
an OMGraphic once and reuse it of for different projection changes.

Then, get your data into an OMGrid object, create/use an
OMGridGenerator that creates a visualization to your liking.

Hope this helps,


On Feb 15, 2007, at 5:39 AM, Jeroen van Dijk wrote:

> Hello,
> I'm working on a crime simulation project that uses the simulation
> framework Repast. This framework has openmap integration which I
> want to
> exploit to plot known crime incidents by a sort of density surface or
> hotspot layer. On the homepage of OpenMap there is this image:
> This image seems to show some
> of this functionality. However, I am not able to find the right
> information on these functions. Can someone give me some hints here?
> When I used google I was overwhelmed by all kinds of irrelevant
> information.
> So in short my question is:
> Is there some kind of density surface layer or hotspot layer
> functionality? If yes, where can I find an example, tutorial, etc?
> Thanks in advance,
> Jeroen
> --
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Don Dietrick,
BBN Technologies, Cambridge, MA

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Received on Thu Feb 15 2007 - 11:06:58 EST

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