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

[ZPO]

Curt,

I'm finally back in the US after 3 years in Baghdad.  I'm living down
in Olympia and working at Ft. Lewis.  Xastir with DRGs was a definite
winner last week when I was running all over the range trails at YTC.

I did a bit more googling and found "geotiffcp" which is exactly like
"tiffcp", but for geotiffs.  DOH!!!  I guess I should have looked a
bit harder.  I can download the unmodified files, but the ones I tried
didn't seem to tile together properly.

I've got another trip coming up next week.  Hopefully I'll have some
downtime at the hotel to try a few different combinations of
"geotiffcp".

When you say the Xastir code is written to handle lines, do you mean
scanlines are strips as defined in the tiff/geotiff spec?

I should be much more active again now that I'm back in CONUS.

73 N5VFF - Brian


On Thu, May 29, 2008 at 10:09 PM, Curt, WE7U <archer at eskimo.com> wrote:
> 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
>  Lotto:  A tax on people who are bad at math. - unknown
> Windows:  Microsoft's tax on computer illiterates. - WE7U.
> The world DOES revolve around me:  I picked the coordinate system!"
>