[Xastir] Compression algorithm problem with DRGs

[Tom Russo]

On Sun, Mar 28, 2004 at 07:49:23PM -0800, a Mr. Richard Feyler of Fort Lee, New Jersey <jeepin95 at comcast.net> writes 'Dear Rosanne Rosannadanna':
> Sorry if this has been asked, I looked through the archives as best as I
> could but didn't find an answer to this question.
> 
>  
> 
> I'm having problems loading geotiff files in Xastir 1.3.1 CVS (from last
> week) while working in Windows (Cygwin) and in Linux (Fedora Core 1). The
> problem I'm having is with virtually all of the DRG files I've downloaded.
> The error I'm getting is as follows.
> 
>  
> 
> /usr/local/share/xastir/maps/o44123C4.tif: Compression algorithm does not
> support random access.

I have seen this on some files that use packbits compression, but not all
of them.  It appears to be related to the type of projection used, as the files
I saw it happen with were in Lambert Conformal Conic projection, not UTM.  I've
never seen it happen on USGS DRGs that are in UTM.  I am not sure why --- 
perhaps those in UTM projection apparently are easily handled without need for 
random access?  Gerry?

I was able to use geotifcp to rewrite the files with no compression they read 
into xastir cleanly with correct georeferencing.  Once I fixed the identical
error...

> Problem in translating

What does listgeo show on these files?  Bet you dollars to donuts there's
some kind of missing metadata in the geotiff file that makes it impossible
for xastir/libgeotiff to do the transformation from whatever projection the 
files are in to lat/long.  You might be able, with a little work, to reinsert 
the missing metadata if the site from which you got them has a link for that 
metadata.

You can insert metadata into a geotiff file with geotifcp if you spend enough
quality time with the libgeotiff documentation to grok the metadata file 
format.

A Kentucky site I once looked at had tons of geotiff files with *NO* projection
and datum information in them, but did have all the metadata needed on a 
separate, human readable web page.  You can read about that experiment in the
archives of this list if you go back about six months to a year, I think.

-- 
Tom Russo    KM5VY     SAR502  DM64ux         http://www.swcp.com/~russo/
Tijeras, NM  QRPL#1592 K2#398  SOC#236 AHTB#1 http://www.qsl.net/~km5vy/
 "It is inhumane in my opinion to force people who have a genuine
  medical need for coffee to wait in line behind people who apparently
  view it as some kind of recreational activity."  -- Dave Barry