I was wondering if anyone knows of any FOSS tools to animate cartograms?
By this, I mean 'tweening' between the geographic shapefile and the cartogram version of a shapefile.
This means gradually changing / morphing / interpolating one polygon into another. The "before" and "after" polygons have identical numbers of nodes, but each of these nodes will have different positions.
There's an example here on the ESRI blog.
They don't do the animation uniformly, they pass across the polygons in increasing longitude order, but it gives an idea of the effect I'm after.
I've been using ScapeToad to do cartograms, and it looks as if it generates a cartogram shapefile with the same number and order of vertices as the original shapefile.
This means I should be able to write code that interpolates each node along a line from its geographic position to its distorted position - perhaps with 'easing' (so the position on the line isn't linear interpolation, more like points on a sine-wave)
Is there already a library or plugin which can interpolate polygons in this way?