Ideas on MapServer bugs 1353/1355 - labels on tiled maps

[Stephen Woodbridge]

Hi all,

I have been playing with the ka-map tiled maps and have been thinking
about the label issues around the tile edges. See MapServer bugs
1353/1355 for more information.

If you are not familiar with this, basically a large meta tile is
generated with an extra edge around the outside of the meta tile, then
individual tiles are extracted from the meta tile. The problem is with
labels on the outside edges of the meta tile. These are sometimes split,
or duplicated between the adjacent tiles

1) define the tile edge keep out zones as big rectangular labels in the
cache and the other labels will avoid them. But I think this just moves
the edge condition to the edge of the keep out zone. This might work
best if the keep out area is larger the the area that will get clipped off.

2) If a label collides with keep out zone, than mark it as drawn but
don't add it to the labelcache. If we fail the placement then mapserver
will try alternate positions with position auto and this causes
duplicate labels along the tile boundaries. The cost of this strategy is
that some labels along the meta tile edges may not get rendered.

3) make the border area larger and through away more area when
extracting the tiles.

4) change the placement rules inside the buffer area so there is higher
likelihood that labels generated in two adjacent meta tiles will align
when tiles from adjacent meta tile are extracted.

Anyway, I offer these ideas as food for thought and some alternate
strategies for you guys doing all the coding. BTW, Great work!

-Steve