[Xastir] Announcing tile support for OSM

[Fred Hillhouse]

> > I am wondering, though, if there is a way to download a 
> large area of 
> > tiles explicitly for offline use?
> 
> I just thought of a sneaky way:  Write a Perl or Python 
> script which uses xastir_udp_client to send packets into 
> Xastir.  Set up Xastir to track the object.  Have the object 
> run along the map in a zig-zag pattern across the area of 
> interest.  Repeat at each zoom level you're interested in.  
> That will force caching of the tiles of interest.  Yea, you 
> can tell I lost too much sleep last night playing with code...
> 
> Of course it would be easier/more efficient to write a block 
> of code for Xastir to just snag the tiles over a region and 
> between two zoom levels.  Or a separate outside program to do 
> the same and then force Xastir to think it cached them.
> 

I run a GPS simulator for times when panning around does not really serve me
well. The simulator sends a GPS sentence (RMC) from one serial port into
another every 1-5 seconds to simulate motion. I use the simulator for
APRSIS32 and ExpertGPS. APRSIS32 uses the OSM tiles and ExpertGPS uses the
Terra Server tiles.

For long trips, such as a recent one from NH to AR, I use Google maps to
route the trip. I can modify the route by dragging the blue line, such as to
avoid New York City for NH to AR, then I submit it to GMaptoGPX [FULL is
selected]. The resulting text is saved in a GPX file and sent by the
simulator to the appropriate software.

If you are unfamiliar with GMaptoGPX, you can check it out here:
http://www.elsewhere.org/journal/gmaptogpx/

I create files for gridsquares on occasion. I mainly do this to grab the
area around where I live and play. I create this file with Excel and my
increment is 1 minute (distance).

Since the tiles servers are not instantaneous, I slow down the timer to run
the simulator at a slow speed. Moving once per second or every few seconds
spreads out the retrieval over a much longer period of time. If tiles are
not queued, then movement will need to be slower or the path will need to
run more than once.

I limit the amount of area retrieved at one time.  For instance, I typically
only retrieve one quadrant of a gridsquare at a time, such as FN42-SW or
FN42-NE. I am not sure this is really needed but it can't hurt. Besides
there is a lot of time my system is not dealing with me, like when I sleep.

APRSIS32 grabs a couple levels of zoom at a time. I set it to zoom level 14
because it will also grab level 15. ExpertGPS only grabs the zoom level
currently displayed. But it does use the same level for a few displays.

I don't know if what I am doing falls within the retrieval guidelines or
not. I know of no way to know. If I exceed the limits and get shut off, I
would not be liking it.


Best regards,
Fred