Determine if a point is inside a triangle formed by 3 points with given latitude/longitude?

Question

I have 3 points (lat, lon) that form a triangle. Using javascript, how can I find if a point is inside this triangle?

Answer 1

One way to determine if a point is inside a triangle is by computing barycentric coordinates:

function vector(from, to) {

return [to[0] - from[0], to[1] - from[1]];

}

function dotProduct(u, v) {

return u[0] * v[0] + u[1] * v[1];

}

function isPointInTriangle(p, a, b, c) {

const v0 = vector(a, c);

const v1 = vector(a, b);

const v2 = vector(a, p);

const dot00 = dotProduct(v0, v0);

const dot01 = dotProduct(v0, v1);

const dot02 = dotProduct(v0, v2);

const dot11 = dotProduct(v1, v1);

const dot12 = dotProduct(v1, v2);

// Compute barycentric coordinates.

const invDenom = 1.0 / (dot00 * dot11 - dot01 * dot01);

const u = (dot11 * dot02 - dot01 * dot12) * invDenom;

const v = (dot00 * dot12 - dot01 * dot02) * invDenom;

// Check if point is in triangle.

return (u >= 0) && (v >= 0) && (u + v < 1);

}