Adapted from this, to avoid the second projection and make flying arc height proportional to length.
Because the ‘sky’ projection is just a scaled up version of the original one, the projection of a sky point in canvas coords can be easily calculated by scaling the ground projection point along the vector from the origin.
Another improvement(?) might be to avoid the swoosh/interpolate function by doing this same trick directly on the stream of points that comes from the normal projection path function.