@twpayne/xcscore

xcscore

Cross country league flight scoring for paragliding.

Introduction

xcscore computes the highest scoring flight from an array of coords according to the World XContest and Swiss Cross Country Cup rules. It is designed for use in XC flight planning software like XC Planner. It uses crude brute force algorithms that support only a small number of coordinates and is not suitable for scoring flights from GPS tracklogs.

API overview

xcscore exports two functions:

• scoreWorldXContest for scoring flights according to the World XContest rules.
• scoreCHCrossCountryCup for scoring flights according to the Swiss Cross Country Cup rules.

Each function takes a single object as an argument with two properties:

• coords: an array of coordinates.
• distKMFunc: a function that returns the distance in kilometers between two coordinates.

Each function returns a single object describing the highest scoring flight found with five properties:

• flightType: the type of the flight, e.g. "openDist", "flatTri", or "faiTri". For a full list of flight types see the documentation.
• dist: the scoring distance of the flight.
• multiplier: the scoring multiplier for the type of flight.
• score: the score of the flight. Note that this is not necessarily equal to the product of dist and multiplier due to rounding rules.
• coords: the coordinates of the start, up to three turnpoints, and end of the scoring part of the flight.

If no scoring flight can be found (e.g. because there are fewer than two input coords) then the returned object will have flightType "none", dist, multiplier, and score 0, and coords [].

For a full description of the API, consult the documentation in the dist/docs directory.

Performance

xcscore uses simple brute force algorithms for implementation simplicity and minimal code size. CPU usage increases with O(N^5) and memory usage with O(N^2) so xscore is heavily CPU bound.

The package includes benchmarks to measure performance, the results of which depend heavily on the CPU. As a rough guide, 25 coords is fine on any machine (scored in approximately less than 2ms on a single core of a 2014-era MacBook Pro), whereas 50 coords is a reasonable upper limit (taking 60ms on the same machine).

More sophisticated algorithms are used for scoring real GPS tracklogs with tens of thousands of points. Contact the author for details.

Use with popular JavaScript mapping libraries

xcscore is independent of the coordinate format and the function to compute the distance between two coordinates. As such, it can be used with any mapping library.

Google Maps JavaScript API

coords can be an array of google.maps.LatLngs and you can use the following function as distKMFunc:

function distKM(latLng1, latLng2) {
    return google.maps.geometry.spherical.computeDistanceBetween(latLng1, latLng2, 6371);
}

LeafletJS

coords can be an array of LatLngs and you can use the following function as distKMFunc:

function distKM(latLng1, latLng2) {
    return latLng1.distanceTo(latLng2)/1000;
}

License

MIT