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20000811: Unidata-Wisconsin datastream additions: CIMSS products (cont.)

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  • Subject: 20000811: Unidata-Wisconsin datastream additions: CIMSS products (cont.)
  • Date: Fri, 11 Aug 2000 11:46:08 -0600
>From: "D. J. Raymond" <address@hidden>
>Organization: NMT
>Keywords: 200008021927.e72JReT03751 ldm-mcidas pqact.conf ldmd.conf pnga2area

Dave,

>I think that I have the reading of the new png satellite files from
>the mcidas stream sorted out.  It was actually pretty simple, as the
>new pnga2area does all the png decoding.

Right.  So the modifications you would have had to make are from reading
delta-encoded images to reading standard AREA files.

>I just had to (1) throw
>out the ``sync'' checks in my reader, and (2) throw out the delta
>decoding stuff in favor of a straight data transfer when reading the
>image part of the file.  Does this make sense to you?

Yes, it does make sense since the delta encoding scheme was implemented
line-by-line.  Now that the images are decoded into the AREA file
format, you simply start reading lines at the beginning of image data.
The "shape" of the image is defined in the AREA file header by the
number of lines and elements, so it is really easy to view the image
data as a rectangular grid of data values.  The other thing that you
have to pay attention to is the fact that the data may be be
represented by one, two, or four bytes.  This is also specified in
the AREA file header.

One of the good things about the PNG format is that you can use
packages like ImageMagic to display the image from the compressed
file.  All that is needed is to strip off the McIDAS headers (AREA
directory, navigation block, comment cards) and then use the 'display'
function.

>Regards,

Sounds like things are going smoothly for you.  Please let me know if
this is not the case.  I am still anxious to turn off the UW stream
broadcast of the delta-encoded images, but I am waiting on a number of
sites that have not yet downloaded the latest ldm-mcidas release.
Right now it looks as if the dual broadcast will have to continue into
September.

Tom