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[McIDAS #ZAW-982854]: (No Subject)

Hi Ben,

> We are trying to use the McIDAS (UNIWISC) imagery without using any
> third party software.

This will be a challenging endeavor especially for imagery whose naviagation
is complex (e.g.,  GOES).

> We are starting with GOES visable.  I am able to
> get the imagery we want from the LDM feed and find the png image portion
> from the file,

It would be best to uncompress the imagery using the 'ldm-mcidas' "decoder"
pnga2area.  Images being received by the LDM at USU (allegan.gis.usu.edu or
webcat.gis.usu.edu) have been configured to decode the PNG compressed images
upon receipt, so it would be easy for you to grab the already processed
images.  The reason I suggest starting here is so that AREA file documentation
can be used directly without worrying about the change made in the compression
process that uses PNG.

Please note that the images are not simply compressed using PNG.  Instead,
the original image headers are preserved in an uncompressed state, and the
image trailer (so called comment card section) is moved from the end of
the image to just after the last header portion.  The image pixels itself 
are the only part actually compressed using PNG.

> however I could use a little help with how to obtain the
> georeference information so that I know where I'm looking at, and can
> correctly overlay with other imagery.

First, please start by uncompressing the image using 'pnga2area'.  Next,
pleases look through the AREA file documentation contained in various places
on the Unidata McIDAS web site:

Unidata McIDAS-X HomePage

  McIDAS-X Documentation and Training

    Miscellaneous McIDAS documents

    McIDAS Programmer's Reference Manual (SSEC)

The Programmer's Reference Manual contains descriptions of the various
types of navigations supported in McIDAS.

> From what I've read, I believe
> the information I would need to do this is in the navigation block.


> However, I'm not familiar with the majority of that information, and
> don't know for sure what it would take to extract coordinate information
> from there.

This will be the challenging part for imagery like GOES.

> So my questions to you are:  Is the navigation block the
> correct place to go to get the georeference information (and if not,
> where should I be looking)?


> Can you give me any direction/advice for
> accomplishing what we're trying to do (overlay the imagery over
> georeferenced maps)?  Specifically how I can get the georeference
> information in a useable form. 

The Programmer's Reference Manual will be the most valuable resource in
this endeavor.

Quite frankly, the easiest thing you could do is use an existing application
that already has been developed to be able to use the navigation contained
in images in AREA file format.  Of course, I would suggest the use of
McIDAS itself or the Unidata Integrated Data Viewer (IDV).  The IDV
is a relatively new offering from Unidata that is written completely in
Java so it runs on any machine on which Java 3D is supported.

If you are not interested in using an existing package (as you said above),
the second easiest thing to do would be to remap the images from their
native projection (GOES/GVAR) into something like rectilinear (even spacing
of image points in Lat and Lon).  McIDAS can be used for this very nicely.
If you are determined to develop a homebrewed solution, you must be prepared
to learn how to handle complicated navigation modules like the one for GOES.

> By the way, I assumed the correct
> "image specific characteristics" to be GOES-7
> [http://www.ssec.wisc.edu/mcidas/doc/prog_man/2003/formats-8.html#11560]
> ).

If you are talking about current imagery, you will need to review the section
on GVAR Imager:


> I appreciate any help/direction you can provide.

Please let me know if/when you have additional questions.

> Thank you!
> Ben Banham

No worries.  Best of luck!


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Ticket Details
Ticket ID: ZAW-982854
Department: Support McIDAS
Priority: Normal
Status: Closed

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