[Xastir] Large Maps

[Tom Russo]

On Mon, Apr 11, 2005 at 09:05:00AM -0700, we recorded a bogon-computron collision of the <archer at eskimo.com> flavor, containing:
> On Mon, 11 Apr 2005, Andrew Rich wrote:
> 
> > I have come across some large mosaic maps topographical maps for xastir.
> >
> > How does it (xastir) go with 660Mb image files ?
> 
> It should theoretically work.  If you could chop it up into small
> tiles it'll work much better though.
> 
> Xastir keeps an index for your maps containing the bounding
> rectangle for each map.  If a map doesn't fit in your viewport, it
> is skipped during map loading.
> 
> If you have one large map, Xastir will have to run through the
> entire file each time you pan or zoom.

If these are GeoTIFF files you can probably read them into xastir even
though they're tremendous.  But, in addition to the issue that Curt brings
up, there are other reasons not to use such monster rasters.

If the map is in unprojected geographic coordinates (lat/lon), the 
scan-line skipping that makes UTM maps go faster is disabled (mainly because
I ran out of time to figure out how to change the algorithm to make it work on 
such rasters).  And if the map is NOT in lat/lon, the approximation used to 
optimize small UTM rasters breaks down and the interior points of the raster
can be in noticable disagreement with vector layers.

-- 
Tom Russo    KM5VY     SAR502  DM64ux         http://www.swcp.com/~russo/
Tijeras, NM  QRPL#1592 K2#398  SOC#236 AHTB#1 
 "The only thing you can do easily is be wrong, and that's hardly
  worth the effort." -- Norton Juster