Tue, Nov 29 2005
11:31:18
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Request created by guest
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Subject: compressed files unreadable (also in V 6.1)
Platform: WindowsNT/2000/XP
grass obtained from: Mirror of Trento site
grass binary for platform: Downloaded precompiled Binaries
GRASS Version: 5.4 and 6.1
Hi
I'm a neophyte to the cygwin-grass environment, but I have had quite a lot of
GIS & DOS experience. I have been using a legal version of Idrisi32, but will
soon be loosing this access & wanted to move onto Grass to allow me a legal GIS
system. Due to the various mirror sites having incomplete copies of both cygwin
& grass I ended up downloading 3 versions of cygwin & 3 of grass (2 of 6.1 &
one of 5.4, plus the spearfish 5.4 tutorial stuff). I have got most of the necessary
files (mainly dll files missing) & can run grass & nviz. I have however had a
serious problem with grass data file compression:
1. grass saves the files in compressed format - this is fine, except that, having
written the imported files (r.in.ascii/r.in.bin/r.in.tiff) it can't read them.
What is worse, when I created a composite file, it too couldn't be read. The
problem seems to be in the writing of the compressed format. The spearfish data
which I downloaded can be read OK, even though they are in compressed format.
r.compress -u run with a spearfish image decompresses the file. However, if I
re-compress it with r.compress it then it can no longer be opened, or decompressed.
This happens using both the 5.4 version and the 6.1 version, which doesn't make
sense, unless the problem is with a cygwin file. The source code of r.compress
only directs me to grass *.exe & C files.
In the case of the Spearfish files, the re-compressed files are larger than the
original compressed file:
Spearfish compressed file (as downloaded) "geology" = 8545 bytes
Uncompressed "geology" = 26600 bytes
Recompressed "geology" = 8633 bytes
I realize this is not technically a Grass bug, but if someone familiar with the
system could tell me which programme files are responsible for the actual compression,
I could try changing them - clearly the zip file is writing a file that is unreadable
by the unzip file. Possibly of help is that some of the spearfish comprssed files
are not read correctly & one gets dropped lines. These files cannot be decompressed
with r.compress. The lines that give problems vary with each session, suggesting
they are not inherent in the raster file. I also had that problem with some of
the files I imported (I cheated - I deleted the compressed file created by Grass
and replaced it with the Idrisi RST file, which is a straight binary file. This
cheat only worked with byte files), which can be returned to Idrisi where they
run OK.
Is it also possible to specify to Grass that it should not compress the data
files?
2. Nviz - the 5.4 version works fine. The 6.1 version takes a long time to load,
the "panel" button doesn't work and having worked from the "eye" to the "center"
option (or to the "fly" option) you can't get back - ie you get one chance only!
This problem does not concern me at the moment, but I put it in for interest.
My machine isn't very fast (700MHz) & only has 256Mb memory, but I'm sure this
doesn't explain everything.
Thanks
Ian Newton (Cape Town)
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Tue, Nov 29 2005
14:06:32
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Mail sent by glynn@gclements.plus.com
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Glynn Clements <glynn@gclements.plus.com>
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Tue, 29 Nov 2005 13:06:27 +0000
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grass5@grass.itc.it
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Subject |
Re: [GRASS5] [bug #3866] (grass) compressed files unreadable (also in V 6.1)
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<20051129103118.651551006B7@lists.intevation.de>
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Request Tracker wrote:
> this bug's URL: http://intevation.de/rt/webrt?serial_num=3866
> -------------------------------------------------------------------------
>
> Subject: compressed files unreadable (also in V 6.1)
>
> Platform: WindowsNT/2000/XP
> grass obtained from: Mirror of Trento site
> grass binary for platform: Downloaded precompiled Binaries
> GRASS Version: 5.4 and 6.1
> 1. grass saves the files in compressed format - this is fine, except
> that, having written the imported files
> (r.in.ascii/r.in.bin/r.in.tiff) it can't read them.
The usual reason for this happening on Cygwin is that the files are
being accessed in "text" mode (i.e. subject to conversion between DOS'
CRLF and Unix' LF). The files in the GRASS database directory must be
accessed in "binary" mode. Use the "mount" command or the CYGWIN
environment variable to control this.
--
Glynn Clements <glynn@gclements.plus.com>
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Tue, Nov 29 2005
14:54:30
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Mail sent by Ian@SCIENCE.uct.ac.za
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Tue, 29 Nov 2005 15:54:23 +0200
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UCT Staff Member - Ian <Ian@SCIENCE.uct.ac.za>
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Subject |
Re: [bug #3866] (grass) compressed files unreadable (also in V 6.1)
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Thank you, I'll give your suggestion a try.
Ian
--
_______________
Ian Newton
Archaeology Department
UCT
650-3819
"When a straight line, the mathematical evidence of a law,
failed to appear on the paper, I suggested different kinds
of logarithmic paper. If you cannot simplify the curve on
one kind of paper, simplify the paper"
von Karman, quoted by Mandelbrot.
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Tue, Nov 29 2005
18:24:12
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Status changed to resolved by mneteler
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