i.tape.other extraction question

[Michael Shapiro]

GRASS does automatic compression of  raster  files  as  they  are
created.  What  you are seeing is the result of this compression.
The compression is not perfect so  a  file  might  get  a  little
larger  (but not a lot larger). Usually they get smaller. Imagery
usually gets larger (ie, doesn't compress well) but you  seem  to
have  had  good  luck  with  your  images.  If  you  wnat them in
uncompressed form, run

	r.compress -u map

or just
	r.compress

and it will ask for the map to be compress/uncompressed.  If  the
map is compressed it will uncompress it. If it is uncompressed it
will compress it.

|
|
|I have used i.tape.other to read some imagery files.  Since I don't have a
|tape drive, I read them from disk files, which works fine.  My question is
|about the SIZE of the created imagery files.
|
|The original data is 4 bands of Landsat MSS data, 2340 lines by 3469 pixels
|(or samples) per line.  The resulting number of rows and columns in the new
|GRASS imagery file SHOULD be
|
|2340 x 3469 = 8117460 total samples = 8117460 bytes of data per band
|
|What I get as output from i.tape.other, however, are files of these sizes:
|
|-rw-r--r--  1 grass40   4933175 Nov  3 17:39 congo_mss_a.1
|-rw-r--r--  1 grass40   6192527 Nov  3 17:40 congo_mss_a.2
|-rw-r--r--  1 grass40   7874113 Nov  3 17:42 congo_mss_a.3
|-rw-r--r--  1 grass40   7119734 Nov  3 17:43 congo_mss_a.4
|-rw-r--r--  1 grass40   8129165 Nov  3 17:50 congo_mss_a.754
|
|Question 1:  Why isn't each file 8117460 bytes in size?
|
|Question 2:  Even more interestingly, why aren't the files AT LEAST all the
|             SAME size, since they contain identical amounts of data and were
|             obtained from the same source file???
|
|             The file named "congo_mss_a.754" is a 3-band color composite
|             image, which SHOULD be 3 x 8117460 bytes = 24352380 bytes in size.
|
|Question 3:  How are these files formatted?  When I try to read them (the
|             OUTPUT files from i.tape.other) with another software package
|             (IDIMS), reading them as lines and pixels (= rows & columns)
|             of data, they look like garbage.  Do they contain header
|             information, or what?
|
|Thanks for any help you can provide!
|
|---Cleavy L. McKnight
|   Department of Geology
|   Baylor University
|
|   cleavy2 at earthlogic.baylor.edu
|
|


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Michael Shapiro                        U.S. Army CERL                  
email:   shapiro at amber.cecer.army.mil  Office of GRASS Integration
phone:   (217) 373-7277                P.O. Box 9005                   
fax:     (217) 373-7222                Champaign, Ill. 61826-9005
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