20010410: NIDS Data Format (cont.)

>From: "charles h. murphy" <address@hidden>
>Organization: Kean University
>Keywords:  200104051732.f35HWHL25802 NEXRAD Level III format

Charlie,

>Thanks for the info on the Nexrad level III format.

No problem.

>The reason I am interested is that we have an adjunct 
>with GIS experience and he was interested in seeing if 
>it is possible to get the radar data into a ArcView
>format. I thought that was interesting so I said I'd
>look into it.

OK.

>Right now as a start I'm using Python which has 
>zlib functionality.  I haven't had any real luck
>so far - hence I think I need to look at the McIDAS
>code to see if I can figure things out.

I remember that there were email exchanges on the ldm-users email list
regarding a Perl (I think) method of uncompressing the NEXRAD Level III
products from NOAAPORT.  You might want to peruse the ldm-users-list
archives to get the code that was posted.  Using that code, you would
end up with an uncompressed NEXRAD product.  At that point you would
still have to know how to read the thing.

>Therefore: which McIDAS source modules should I
>look at for (1) the decompression of the files,
>and (2) reading the decompressed data.

You would need the latest version of McIDAS from us, and you would look
in the C module nexrutil.c.  The routines to look at in nexrutil.c are:

GetNexrDirs
ReadNexrInfo
GetZlibedNexr

The last module is the guy that uncompresses the zlib blocks in the
image.  It even has a nice little diagram of what the zlib compressed
product looks like.

>Thanks,

Talk to you later...

Tom