As in https://www.flickr.com/photos/walkingsf/sets/72157628616533659
Requires the "cart" cartogram tool with my slight modifications at https://github.com/ericfischer/cart
Put that in a sibling directory to this one and
( cd ../cart; make cart interp )
With a file containing lines in this format:
user date time lat,lon
For example,
curl -O http://sfgeo.org/data/tourist-local/1-RESIDENT.gz
Accumulate a grid of density:
cc -g -Wall -O3 -o gather-density gather-density.c -lm
zcat 1-RESIDENT.gz | ./gather-density > density
The end of the output will look like
1000 1000
51.366408 -0.324268 51.584092 0.025234
Keep those numbers. You will need them.
Then make a cartogram, using the "1000 1000" part as the bounds:
../cart/cart 1000 1000 density density.out
cc -g -Wall -O3 -o mapback mapback.c -lm -ljpeg
zcat 1-RESIDENT.gz | ./plot-motion | ./invert 1000 1000 51.366408 -0.324268 51.584092 0.025234 | ../cart/interp 1000 1000 density.out | ./mapback 1000 1000 density.out
And at the end you should get a file called out.jpg with the wispy image.
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