>From: address@hidden >Organization: GMU >Keywords: 200411231749.iANHn27j024490 McIDAS AREA GVAR navigation Hi Ying, I finally got some time to respond to your message. Sorry for the delay. >I want to read the GOES 12 data downloaded by LDM. Until now, it's no >problem to display the picture by reading out the data block in the >file. But I'm not sure about the navigation block, which contains the >information to geolocate the image. To be sure we are clear, the images that are transferred by the LDM in the UNIWISC (aka MCIDAS) datastream are PNG compressed AREA files. The various headers included in a standard AREA file are contained at the beginning of the product followed by the comment card section that usually is found at the end of an AREA. The last portion of the product is a PNG compressed image. >From the link >http://my.unidata.ucar.edu/content/software/mcidas/miscdocs/area.html >on Page 19, it says the word 1 of NAV block will be >'GOES'/'PS'/'LAMB'/' '. But what I found from my file is 'GVAR'. area.html is old. area2.html contains makes reference to GVAR: McIDAS miscellaneous docs http://my.unidata.ucar.edu/content/software/mcidas/miscdocs/misc_docs.html Description of AREA file format for GOES GVAR, GOES-7 and METEOSAT PDUS http://my.unidata.ucar.edu/content/software/mcidas/miscdocs/area2.html >So I'm not sure if the explanation of other words is correct for my >file. Please use area2.html, or consult the McIDAS Programmer's Reference Manual: McIDAS Programmer's Reference Manual (SSEC) http://www.ssec.wisc.edu/mug/prog_man/prog_man.html >The GOES data is in it's own projection called "GVAR projection", >right? The current satellite images in the IDD UNIWISC stream are from the GVAR series of GOES platforms, yes. >How can I do the projection transformation so that maps from >other sources can be layered on top of it? You would have to write code that can interpret the navigation parameters and correctly map satellite coordinates to earth coordinates. This is no simple task. The full documentation for the GVAR navigation is contained in documents referenced in the area2.html file: Operations Ground Equipment, Internal Specification, DRL 504-02-1 Part 1, Specification No E007020, released February 9, 1994, Space Systems/Loral, 3825 Fabian Way, Palo Alto, CA, 94303-4604. >Is this projection available in some GIS software like ArcGIS? I don't know if any GIS system supports satellite projections. My understanding is that GIS systems typically deal with conical projections. One possibility is to use the current release of McIDAS which can access data that has the GVAR navigation format and remap it into some conical projection. Then, use a different McIDAS facility to output the image into a format that _is_ recognized by GIS, GeoTIFF. In order to use McIDAS, you would need to register as a Unidata user (which you have already done); download McIDAS; build, install, and configure McIDAS, and hen learn how to use it. This can be daunting since McIDAS is a _big_ package, but once you get the hang if it it is not difficult. >Hope I specified it clearly. Thanks a lot! Again, sorry for the big delay. Cheers, Tom -- NOTE: All email exchanges with Unidata User Support are recorded in the Unidata inquiry tracking system and then made publicly available through the web. If you do not want to have your interactions made available in this way, you must let us know in each email you send to us.
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