[GRASS5] [bug #3866] (grass) compressed files unreadable (also in V 6.1)

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this bug's URL: http://intevation.de/rt/webrt?serial_num=3866
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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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