[Xastir] Terraserver problems with map registration

[Tom Russo]

On Wed, Nov 28, 2007 at 11:01:04AM -0800, we recorded a bogon-computron collision of the <kd7nm at pugetsound.net> flavor, containing:
> It also occurs to me that this might be a file size limit, vs. a pixel count
> limit, so the returned image size may be related to that - though from their
> end, it'd be a lot easier to code a pixel count limit.  If file size was the
> limit, then the file size could vary due to compression factors and how much
> detail is present.

I'm pretty sure that it's a file size limit, not a pixel count limit.  At 
one point when I was exploring this a few years ago, I found that the problem
went away when I was viewing certain areas even though I hadn't changed
my window size or zoom level --- almost certainly because at those areas the 
compression led to smaller files.

The other approach would be to fetch the terraserver-usa images in tiles instead
of as one monolithic image.  That's how teraserver-usa builds its large
images, and is what is happening behind the scenes when we request a large
area.  Also, if we fetch the worldfile and use it properly instead of just
keying off the request data and the file size, we would be assured that 
when we plop a tile down we always plop it where it's supposed to go.

Furthermore, if we did tile-based fetches we could *cache* the tiles and 
speed up zooms and pans.  Right now, if you change the view at all the cached
full image is useless and another one is fetched.  If we used tiles instead,
and checked the cache before downloading, then we'd only have to fetch new
tiles for the areas that were exposed.

> -----Original Message-----
> From: xastir-bounces at xastir.org [mailto:xastir-bounces at xastir.org] On Behalf
> Of Tom Russo
> Sent: Wednesday, November 28, 2007 10:36 AM
> To: Curt, WE7U
> Cc: Xastir at xastir.org
> Subject: Re: [Xastir] Terraserver problems with map registration
> 
> On Wed, Nov 28, 2007 at 10:31:57AM -0800, we recorded a bogon-computron
> collision of the <archer at eskimo.com> flavor, containing:
> > On Wed, 28 Nov 2007, Curt, WE7U wrote:
> > 
> > > On Wed, 28 Nov 2007, Curt, WE7U wrote:
> > >
> > > > At 1410x950 it looks ok.  If I go much bigger in either direction 
> > > > the registration gets knocked out of whack in the E/W direction.
> > >
> > > Looks like 1410x992 is the limit.  Go over that by one pixel in 
> > > either direction and it's off.
> > 
> > Hmmm.  Can go up to 1408x1109 and it's fine too.  Must be larger 
> > vertically before it can go larger horizontally?
> 
> The issue is entirely that the file requested is too large for terraserver
> to agree to serve.  It is likely not a fixed pixel limit, since jpg
> compression probably allows some pizel-wise larger images to be smaller
> byte-wise than others.

-- 
Tom Russo    KM5VY   SAR502   DM64ux          http://www.swcp.com/~russo/
Tijeras, NM  QRPL#1592 K2#398  SOC#236 AHTB#1 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