[Xastir] Re: Bounding boxes

[Curt Mills, WE7U]

On Tue, 14 Oct 2003, Tom Russo wrote:

> As I read the comments in the code, the way the individual pixels of the
> geotiff file are plotted is not *pedantically* correct, but practically it's
> fine --- for speed, each scan line of the geotiff image is mapped onto a
> corresponding rotated/stretched line in the lat/lon system used for plotting
> in the xastir window.  That's not strictly correct, but on these scales I
> can't imagine the precision lost would make it worthwhile to do all the extra
> calculations to get it strictly correct (it already takes an age or more to
> load all the topos I need to cover my local area at high zoom levels, I
> wouldn't want it any slower!).


There are some speedups in the geotiff code as well:  As you zoom
out, it starts skipping more and more of the map's scan lines, based
on the zoom level, to make the loading much faster.

As you zoom in, it skips the scanlines above/below your current view
in order to make loading faster.

What would be good to do is to translate the map into our own format
which would be in the proper projection and in the proper units, as
we import each map.  After that translation we could load things
much more quickly as there'd be less math involved, and we could
also get much better at skipping portions of the image that weren't
on the screen or weren't relevant to the zoom level.

-- 
Curt Mills, WE7U                    hacker_NO_SPAM_ at tc.fluke.com
Senior Methods Engineer/SysAdmin
"Lotto:    A tax on people who are bad at math!"
"Windows:  Microsoft's tax on computer illiterates!" -- WE7U
"The world DOES revolve around me:  I picked the coordinate system!"