public void Drag(Location start, Location end)
{
var d = -start.VectorTo(end);
_pos = _pos.LocationAway(d);
Pos3d = _pos.ToPositionAboveSeaLeveld(_altitude);
LookAt = LookAt.LocationAway(d);
LookAt3d = LookAt.ToPositionAboveSeaLeveld(0);
Dirty = true;
}