[Xastir] Maps won't cache

[Tom Russo]

On Sun, May 10, 2015 at 07:12:44PM -0700, we recorded a bogon-computron collision of the <hal at seanet.com> flavor, containing:
> This smells to me (without looking at the code) like a tile cache size limit problem. I don't know what xastir used to decide how much map data to cache, but that's the setting I would hunt for. 

There is no such setting for OSM map tiles.

In fact, in browsing the code the only place I see that would remove OSM tiles
from the OSMtiles directory does so when the tile is bad.

I'm going to have to fire up Xastir on my laptop (which runs Ubuntu) and see
if I can reproduce Skyler's issue.  I only use Xastir on that laptop for
search and rescue, when I never have internet -- and so I never use online
maps there (I use shapefiles and topo maps in that activity).  It will be
a day or so before I can try that.

> Another idea would be to generate data in advance. I just poked around in mailing list from late 2012 and saw some talk about using Mbtiles data with xastir. Mbtiles is a format for mass offline storage of raster tiles. It's supported by GDAL, and I think that means it works in xastir? You could use a program like Tilemill to generate full Mbtiles coverage for the areas you need. Side benefit (if it works): you can distribute the same Mbtiles file to all of your volunteers, minimizing training load. 

Xastir does *NOT* actually support gdal raster formats, which is why we are 
quick to point out that most uses won't want to bother with GDAL.  There was 
brief bit of development effort in that direction about 10 years ago, but it 
resulted only in the support of OGR vector layers, not GDAL raster layers.  But
the OGR code is akin to the older shapefile code without "dbfawk" --- meaning
that Xastir will only render certain types of ogr data layer nicely, and all
others will just render as ugly black lines.

-- 
Tom Russo    KM5VY   SAR502   DM64ux          http://www.swcp.com/~russo/
Tijeras, NM  QRPL#1592 K2#398  SOC#236        http://kevan.org/brain.cgi?DDTNM
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