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[ldmMcidas #FQZ-585386]: compress AREA

Hi Valentijn,

I hope things are going well for you...

re:
> i'm about to leave for home, so this is a quick one...

OK.

> I'm archiving data in AREA format, and would like to minimize disk
> usage. i read somewhere in the support archives that it is possible to
> compress data. i quote....
> 
> Our PNG compression applications effectively do the following:
> 
> 
> McIDAS AREA:
> 
> +-----------------------+                +-------------------------+
> |        Header         |                |          Header         |
> +-----------------------+                +-------------------------+
> |         Nav           |                |            Nav          |
> +-----------------------+     PNG        +-------------------------+
> |         Cal           |    =====>      |            Cal          |
> +-----------------------+                +-------------------------+
> |         AUX           |                |            AUX          |
> +-----------------------+                +-------------------------+
> |                       |                |      Comment Cards      |
> |                       |                +-------------------------+
> |                       |                |                         |
> |                       |                |                         |
> |     Uncompressed      |                |        Compressed       |
> |         Data          |                |           Data          |
> |                       |                |                         |
> |                       |                |                         |
> |                       |                +-------------------------+
> |                       |
> |                       |
> |                       |
> |                       |
> |                       |
> +-----------------------+
> |    Comment Cards      |
> +-----------------------+

Correct.  The technique I was referring to was the compression of imagery
data in McIDAS AREA files for IDD broadcast of the UNIWISC datastream.
Tests run in-house showed that this technique was better than most other
compression schemes that we tested (e.g., compress, gzip, bzip2).  bzip2
compression was as good and slightly better for some types of images in
some types of weather situtations, but not as good overall.

> We keep both the GINI and AREA header information uncompressed so that
> the header information can be used without uncompressing it first.  For
> instance, a McIDAS ADDE server for either only needs the header
> information to do things like IMGLISTs.

This is exactly the same reason that I compress the UNIWISC images
in the way pictured above.

> The data only has to be
> uncompressed when it is needed by things like IMGDISP, IMGCOPY,
> IMGREMAP, etc.

Yes.  What I never did in McIDAS was write a new ADDE server (or modify
the existing AREA server) to recognize compressed images and uncompress
them on the fly.  One of the reasons I did not do this was I was under
the impression that PNG compression did not allow one to figure out
how much to skip over to get to a starting image line.  I have since
been informed that this is possible.

> Can you give me some directions, and send me the sources please?

The compression routine that I wrote is called 'area2png' and its
corresponding uncompressor is 'pnga2area'.  Both applications are
included in the ldm-mcidas package that is available by anonymous
FTP:

machine:   ftp.unidata.ucar.edu
user:      anonymous
pass:      address@hidden
directory: pub/ldm-mcidas             <- source
directory: pub/binary/<os specific    <- binary
file:      ldm-mcidas-2004-tar.Z

By the way, I need to make a new distribution of the package since
it uses the McIDAS SATANNOT and SATAND files, and SATBAND changed
format in McIDAS v2005.  I have already updated the source, and
can make it available to you so you can use the v200[56] McIDAS
distributions version of SATBAND.  Please let me know if you are
interested.

re:
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Does this mean that you do not want your exchanges with Unidata Support
made publically available?  If you do not, it will mean that answers
we provide to you will be useful on by you, and, therefore, will
limit the leveraging we use in making answers to questions available
to anyone.


Cheers,

Tom
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Ticket Details
===================
Ticket ID: FQZ-585386
Department: Support ldm-mcidas
Priority: Normal
Status: Closed