Improve performance of trimmed(from:,to:)

[jonkan]

So, I found the performance of the LineString.trimmed(from:to:) to be unusably slow and that it's caused by this distance calculation.

Calculating the distance between coordinates i and i+1 can be done with a simple/cheap distance(to:), but instead the LineString.distance(from:to:) is used, which kills performance because it allows from/to to not be on the line and has to calculate which line coordinate is closest using closestCoordinate(to:), a O(n) operation, which leaves trimmed(from:to:) at a terrible O(n^2).

Please let me know if I'm missing anything.

[azarovalex]

@jonkan Thanks for contributing!

Nice catch, looks like we've used the wrong distance method the whole time. Original turf-js repo uses this method for distance and that's exactly the method you use in this PR.

@1ec5 please take a final look at the PR and let's merge this.

[1ec5]

Great catch – this is a tricky part of porting anything from Turf.js to turf-swift, since turf-swift uses object-oriented methods instead of global functions. Thank you for your contribution!

[jonkan]

Happy to help! ❤️