[Xastir] DRG Error: Compression Algorithm Does Not Support Random Access

[Curt, WE7U]

On Thu, 29 May 2008, ZPO wrote:

> I'm having an issue using the WA clipped DRGs from -
> http://rocky2.ess.washington.edu/data/raster/drgclip/index.html - .


> Some of the DRGs load fine, but the majority (especially the 24Ks)
> give an error of "compression algorithm does not support random
> access".

Such is the way of the world with modified DRG's...  At least you
didn't run into MrSID compressed -and- clipped DRG's.


> Based on my reading it appears the correct answer is to reprocess the
> files through TIFFCP and convert them.  I'm unsure whether I should
> convert them to strips or tiles.  It looks like scanline format is out
> since it doesn't allow random access when using compression.  Between
> strips and tiles, is there a preference on which Xastir can process
> more efficiently for pan/zoom/update operations?  At first glance I'm
> guessing tiles would be the most efficient.  Along with the goes the
> question of recommended tile size.  16? 32? 64? 128?

The Xastir geotiff code is written to handle lines, not tiles.

I see two options:

1) Find another source for unmodified DRG's.

2) Do a Google search through the Xastir list to find the
   parameters you need to convert those DRG's to.

Regarding #1:  Where are you at?  I have the complete set of WA
DRG's, unmodified.  I lent out a set of CD's and a set of DVD's to
one Xastir user in Everett.  I have another DVD here at home
somewhere, and another set of CD's at work.  I'd rather keep my
hands on one set of each, but the guy I lent the other sets to
should be done by now.

Another possibility is that you might live near one of the people
I've lent them to before and can copy the DVD's, CD's, or files off
their hard drive.  There are at least 4 or 5 people around mostly
western WA that should have them.

Yet another possibility:  If you're near UW you should be able to go
to the library on campus and copy the CD's.  They might have them
online now, not sure.  I know they have the DOQQ's online and I've
been able to download a few and convert them for use with Xastir.

-- 
Curt, WE7U.				archer at eskimo dot com
http://www.eskimo.com/~archer
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