Get an item id nearest to coordinates. If more than one item is at the
same closest distance (e.g. two items overlap the point), then the
top-most of these items (the last one in the display list) is used. If
radius is specified, then it must be a non-negative value. Any item
closer than halo to the point is considered to overlap it.
Get an item id nearest to coordinates. If more than one item is at the same closest distance (e.g. two items overlap the point), then the top-most of these items (the last one in the display list) is used. If radius is specified, then it must be a non-negative value. Any item closer than halo to the point is considered to overlap it.