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Update osgridref.js #106

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Update osgridref.js #106

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4 changes: 2 additions & 2 deletions osgridref.js
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Original file line number Diff line number Diff line change
Expand Up @@ -86,14 +86,14 @@ class OsGridRef {
const φ0 = (49).toRadians(), λ0 = (-2).toRadians(); // NatGrid true origin is 49°N,2°W
const N0 = -100e3, E0 = 400e3; // northing & easting of true origin, metres
const e2 = 1 - (b*b)/(a*a); // eccentricity squared
const n = (a-b)/(a+b), n2 = n*n, n3 = n*n*n; // n, n², n³
const n = (a-b)/(a+b), n2 = n*n, n3 = n2*n; // n, n², n³

let φ=φ0, M=0;
do {
φ = (N-N0-M)/(a*F0) + φ;

const Ma = (1 + n + (5/4)*n2 + (5/4)*n3) * (φ-φ0);
const Mb = (3*n + 3*n*n + (21/8)*n3) * Math.sin(φ-φ0) * Math.cos(φ+φ0);
const Mb = (3*n + 3*n2 + (21/8)*n3) * Math.sin(φ-φ0) * Math.cos(φ+φ0);
const Mc = ((15/8)*n2 + (15/8)*n3) * Math.sin(2*(φ-φ0)) * Math.cos(2*(φ+φ0));
const Md = (35/24)*n3 * Math.sin(3*(φ-φ0)) * Math.cos(3*(φ+φ0));
M = b * F0 * (Ma - Mb + Mc - Md); // meridional arc
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