[Xastir] Announcing tile support for OSM

[Jerry Dunmire]

Early this morning Curt committed my patches to add tile support for
OSM to the CVS tree (thanks Curt).

Tiles are small (256x256) map sections that get assembled on-the-fly
to make an image that fills the xastir window. Since typical xastir
windows are larger than 256x256, there is a small penalty for the
extra http requests, but a big gain in re-use. Use of tiles is the key
to 'slippy map' implementations in browsers and some newer apps (take
a look at TangoGPS for an example). Tiles also improve the OSM
experience with xastir, just don't expect 'slippy map' performance.
Xastir's strengths like in other areas.

There is an new README file describing OSM that gives a lot more
details on both the static and tiled maps. Please read it carefully.

The default setup provides new OSM*.geo map description files. There
are a mix of tiled and static maps. You can tell the difference by
file name. While any of the OSM based styles could be tiled, the tiles
from CloudMade require an access key. You have to register for at the
CloudMade site to get a key and then modify the appropriate GEO file.

The biggest weakness in the present tiling implementation is that a
slow server, or worse one that does not respond, is a real problem
since for large screens you could have to wait 20 or more tiles to
time out before the display will refresh. The ski trail version of OSM
was giving me headaches with timeouts yesterday- take care.

I am working on a way to cancel the tile downloads, but since most
sites are responsive I don't think you will run into too many problems
(unless you are a skier - hi hi ).

Tiles are separated from the standard Xastir cache so that they can be
shared with other OSM applications. I have successfully shared tiles
between Xastir and TangoGPS. See the README.OSM_maps file for more
details.

 Let me know if you run into problems.

73,
...jerry
KA6HLD