Function _radTanApplyDistortion

src/utils/cameraUndistortion.ts:271–297

(uu: Vec2, i: CameraIntrinsics)

// This differs structurally from THIN_PRISM_FISHEYE (k1–k4 only; prism on uu).

function _radTanApplyDistortion(uu: Vec2, i: CameraIntrinsics): Vec2 {
  const theta2 = uu.x * uu.x + uu.y * uu.y;
  const theta4 = theta2 * theta2;
  const theta6 = theta4 * theta2;
  const theta8 = theta4 * theta4;
  const theta10 = theta8 * theta2;
  const theta12 = theta10 * theta2;
  // 6-coeff radial scale
  const thRadial = 1 + i.k1 * theta2 + i.k2 * theta4 + i.k3 * theta6
                     + i.k4 * theta8 + i.k5 * theta10 + i.k6 * theta12;
  const x = thRadial * uu.x;
  const y = thRadial * uu.y;
  const x2 = x * x;
  const y2 = y * y;
  const xy = x * y;
  const r2 = x2 + y2;
  const r4 = r2 * r2;
  // Tangential on (x, y) — COLMAP convention: i.p1 = COLMAP p0, i.p2 = COLMAP p1
  // COLMAP: dx = 2*p1*xy + p0*(r2+2*x2), dy = 2*p0*xy + p1*(r2+2*y2)
  // Substituting our names: dxTang = i.p1*(r2+2*x2) + 2*i.p2*xy
  const dxTang = i.p1 * (r2 + 2 * x2) + 2 * i.p2 * xy;
  const dyTang = 2 * i.p1 * xy + i.p2 * (r2 + 2 * y2);
  // Thin-prism: x-direction uses sx1,sy1; y-direction uses sx2,sy2
  const dxTp = i.sx1 * r2 + i.sy1 * r4;
  const dyTp = i.sx2 * r2 + i.sy2 * r4;
  return { x: x + dxTang + dxTp, y: y + dyTang + dyTp };
}

/** 2D Newton to solve `_radTanApplyDistortion(uu) = p` for `uu` (numeric Jacobian). */
function _radTanRemoveDistortion2D(p: Vec2, i: CameraIntrinsics): Vec2 {