[Xastir] Slow raster map render

[Tom Russo]

On Fri, Sep 07, 2012 at 10:07:14AM -0600, we recorded a bogon-computron collision of the <esarfl at gmail.com> flavor, containing:
> Why is Xastir slow to render raster maps? I'm curious what is actually
> happening behind the scenes. It appears that Xastir is re-projecting
> the raster maps, requiring an expensive render. 

Yes, that's what's happening.

> Why not just
> re-project the APRS stations and any shapefile overlay to match the
> raster tiles? Wouldn't this be much faster?

Yes, it would, but then you'd have to deal with the issue that many rasters
aren't in the same projection, and the vector overlays are often in something
else, too.  

So the approach is that the Xastir coordinate system is basically Platte Carre
(equidistant cylindrical) with a scaling so that the entire globe is represented
by long integer coordinates.  Everything is done in that coordinate system,
and maps have to be reprojected.


> I normally use Xastir with a USGS topo tiles base layer (from ESRI,
> using the OSM tile loader) with an OSM Cloudmade shapefile overlay.

If you really want topo maps as a base layer, you're better off getting
USGS GeoTIFFs and doing the reprojection once, converting them to WGS84 
lat/lon instead of NAD83 or NAD27 UTM.  This way, no projection is done at 
render time.  You can do the reprojecting using gdalwarp.


-- 
Tom Russo    KM5VY   SAR502   DM64ux          http://www.swcp.com/~russo/
Tijeras, NM  QRPL#1592 K2#398  SOC#236        http://kevan.org/brain.cgi?DDTNM
"And, isn't sanity really just a one-trick pony anyway? I mean all you get is
 one trick, rational thinking, but when you're good and crazy, oooh, oooh,
 oooh, the sky is the limit!"  --- The Tick