This tool is setup specifically to work with the recording devices that are accessible to kitesurfers, namely GPS-enabled smartwatches. For this reason, the tool requires you to enter the wind direction manually, as there are no readily available wind instruments to record apparent wind angle for kiteboards.
As an example of the output, here's a track recorded on Moses 683 wing and a 9m F-one Bandit in ~18-20 knots of wind:
And here's one from a 10m Slingshot SST and a surfboard in the same conditions:
The numbers are speeds in knots. The red area shows VMG up and downwind. The blue area shows actual board speed for every angle relative to the wind.
These were recorded in a river where the current flows upwind, so the VMG looks better than it would in still water.
The accuracy of the graph depends on the consistency of the wind. The shiftier the wind, the less accurate the graph (it will look as if your tack and gybe angles are narrower than they really are) because the tool has no way of knowing the precise wind direction at any given moment along the track. Still, it's useful for comparing different equipment in similar conditions.
You can use the tool yourself here: http://www.tylerkaraszewski.com/polars.html
You can see the code for the tool here: https://github.com/tylerkaraszewski/gpx_polars/
Let me know if you find this interesting, have questions, or discover any bugs or problems with it!
