Created
January 6, 2016 21:20
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| var kmPerDegree = 110; // approximate distance in km per latitude degree and longitude degree on equator | |
| var roundingMask = Math.pow(10, 6); // rounding coordinates to 6 digits after decimal point | |
| export interface ICoordinates { | |
| lon: number; | |
| lat: number; | |
| } | |
| export function toRadians(degrees: number): number { | |
| return (degrees / 180) * Math.PI; | |
| } | |
| // returns a random point anywhere around source point, but not further away than maxDistanceKm | |
| // both input and output points are expressed as latitude/longitude in degrees | |
| export function getRandomPointAround(sourcePoint: ICoordinates, maxDistanceKm: number): ICoordinates { | |
| if (!sourcePoint || !sourcePoint.lat || !sourcePoint.lon) { | |
| return undefined; | |
| } | |
| maxDistanceKm = maxDistanceKm || 1; | |
| var degreeVariationLat = maxDistanceKm / kmPerDegree; | |
| // distance per longitude degree depends on how far away we are from equator (source point latitude) | |
| // the futher away we are, the shorter longitude "rings" become, so less distance per degree | |
| // Math.cos determines this ratio | |
| var degreeVariationLon = degreeVariationLat * Math.cos(toRadians(sourcePoint.lat)); | |
| // random from -1 to +1 | |
| var randomLat = (Math.random() - 0.5) * 2; | |
| var randomLon = (Math.random() - 0.5) * 2; | |
| var lat = sourcePoint.lat + (degreeVariationLat * randomLat); | |
| var lon = sourcePoint.lon + (degreeVariationLon * randomLon); | |
| lat = lat % 90; // latitude has -90 to +90 degree range | |
| lon = lon % 180; // longitude has -180 to +180 degree range | |
| return { | |
| lon: Math.round(lon * roundingMask) / roundingMask, | |
| lat: Math.round(lat * roundingMask) / roundingMask | |
| }; | |
| } |
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