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Polygon centroid - typescript or javascript
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/** | |
* https://en.wikipedia.org/wiki/Centroid#Of_a_polygon | |
*/ | |
public getPolygonCentroid(vertices: number[][]): { lat: number, lon: number } { | |
const centroid: { lat: number, lon: number } = { lat: 0, lon: 0 }; | |
const vertexCount: number = vertices.length; | |
let area: number = 0; | |
let x0: number = 0; // Current vertex X | |
let y0: number = 0; // Current vertex Y | |
let x1: number = 0; // Next vertex X | |
let y1: number = 0; // Next vertex Y | |
let a: number = 0; // Partial signed area | |
let i: number = 0; // Counter | |
for (; i < vertexCount - 1; ++i) { | |
x0 = vertices[i][0]; | |
y0 = vertices[i][1]; | |
x1 = vertices[i + 1][0]; | |
y1 = vertices[i + 1][1]; | |
a = x0 * y1 - x1 * y0; | |
area += a; | |
centroid.lon += (x0 + x1) * a; | |
centroid.lat += (y0 + y1) * a; | |
} | |
// Do last vertex separately to avoid performing an expensive | |
// modulus operation in each iteration. | |
x0 = vertices[i][0]; | |
y0 = vertices[i][1]; | |
x1 = vertices[0][0]; | |
y1 = vertices[0][1]; | |
a = x0 * y1 - x1 * y0; | |
area += a; | |
centroid.lon += (x0 + x1) * a; | |
centroid.lat += (y0 + y1) * a; | |
area *= 0.5; | |
centroid.lon /= (6 * area); | |
centroid.lat /= (6 * area); | |
return centroid; | |
} |
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