Function closestPointPolygon

CesiumGeospatial/src/S2CellBoundingVolume.cpp:260–289

* Finds closes point on the polygon, created by the given vertices, from * a point. The test point and the polygon are all on the same plane. * @private */

 * @private
 */
glm::dvec3 closestPointPolygon(
    const glm::dvec3& p,
    const std::array<glm::dvec3, 4>& vertices,
    const std::array<glm::dvec3, 4>& edgeNormals) {
  double minDistance = std::numeric_limits<double>::max();
  glm::dvec3 closestPoint = p;

  for (size_t i = 0; i < vertices.size(); ++i) {
    Plane edgePlane(vertices[i], edgeNormals[i]);
    double edgePlaneDistance = edgePlane.getPointDistance(p);

    // Skip checking against the edge if the point is not in the half-space that
    // the edgePlane's normal points towards i.e. if the edgePlane is facing
    // away from the point.
    if (edgePlaneDistance < 0.0) {
      continue;
    }

    glm::dvec3 closestPointOnEdge =
        closestPointLineSegment(p, vertices[i], vertices[(i + 1) % 4]);

    double distance = glm::distance(p, closestPointOnEdge);
    if (distance < minDistance) {
      minDistance = distance;
      closestPoint = closestPointOnEdge;
    }
  }

  return closestPoint;
}

} // namespace