Heatmaps

[Hai-Etlik]

So, one of the things I was working on recently at work was logging the bounding boxes of WMS requests made to GeoServer. This obviously made for a lot of overlapping boxes, which is hard to display with normal symbolization. Geoserver does however have some interesting alternative forms of symbolization, including something called a "heatmap" This is a surface made by drawing the centres of the features into the map and keeping track of how many times they overlap. Then the whole surface is blurred. Then the whole thing is normalized so the maximum ls 1.0.

Now that normalizing of overlapping levels is really useful, but I needed to preserve the shape. With a bit of work though, I was able to make two changes. Making it render the bounding box of a feature, and normalizing the minimum as well as the maximum to preserve contrast when zooming in.

The result looked like this



Now, bounding boxes are nice and all I needed for the project I was working on, but it would be even better to render the feature properly. because of the way Heatmap works, it can't just leverage a stock graphics library like Java2D (which most of the rest of GeoServer uses for vector to raster.)

I didn't have time for polygons (at this point I was on my own time), but rendering a linestring is pretty straight forward. So I added that, took some GPS tracks from my time delivering pizza, and got a pretty cool looking map.