19990802: Displaying terrain overlays in Gempak (fwd)

>From: David Ovens <address@hidden>
>Organization: .
>Keywords: 199908021603.KAA27427

>> Justin, the topo images are in AREA file format, same as the McIDAS
>> satellite images. 
>> 
>> If you have raw lat,lon,elevation data, then you can use mcidas to
>> convert the data into an AREA file. Once you have an area file, you can
>> create
>> a color lut file for gempak to use as the enhancement.
>> 
>>...
>> Steve Chiswell
>
>Hello, Steve,
>
>I am probably the most well-versed in Mcidas here, but I don't know
>how to convert data into an AREA file in Mcidas.  Is there a separate
>utility or a Mcidas function call to do this?  I am excited about
>creating these topographic overlays using our 1-km terrain dataset and
>will be happy to send some back to you for wider distribution.
>
>Thanks,
>
>David
>-- 
>
>David Ovens            e-mail: address@hidden
>(206) 685-8108
>Dept of Atmospheric Sciences, Box 351640
>University of Washington 
>Seattle, WA  98195
>

David,

We would welcome any contributions back.

I am looking back through a past exchange that Tom Yoksas had in the 
Mcidas support email archive with John Horel at Univ. Utah where he
discussed converting topo data into an area file. Basically, the data is
in a binary "raster" format, in this example 2 byte values of
elevation data.

------ Cut from http://www.unidata.ucar.edu/glimpse/mcidas/3090 -----
>here's what i think we should be doing for a flat file of terrain data
>(temp.dat) which is a 2x2 lat-lon grid with 241 lines (lat) and 241
>elements (lon). the 2x2 square is for 39 to 41 n and 113 to 111 w

>makearea.k temp.dat 9999 241 241 0 2 0 20000



I assume that there is no header bytes that must be skipped in order to
get to the topography values (the 0 after 241 241).  I further assume
that the elevation data is two byte data (the 2 after the 241 241 0).
Finally, I assume that that the range for the elevations is correct (0
20000 meters?).  It is likely that the data don't range between 0 (meters ?)
and 20000 (meters ?) over the area of interest for you.  The inclusion
of these command line options allows you to get the most resolution of
the data into the output 256 "brightness" levels that will be included in
the output AREA file.

>maknav.k 9999 RECT= 1 39 1 113 .008333 .008333
>
>or some such.

Right.  After the AREA is made, you would then setup its navigation block
using MAKNAV.  The parameters you specify look correct to me.  The proof
will be in the registration of maps to the image after it is made.

The good news is that you can run MAKNAV, DF (to display the image), and
MAP repeatedly in your McIDAS-X session until you have good navigation
(good comparison between landmarks and the MAP that McIDAS will draw).

-----------------------------------------------------------------------

The above represents converting a raster of values that represent a lat/lon
projection- hence maknav specifying a rectilinear projection, where the first
line/element is 1,1 with lat/lon 39.00N 113.00W and the dlat/dlon is .008333
degrees.

Depending on your data, you may need to do some work to create an output file 
of your terrain values into the binary raster.

Hope this gives you a good start-

Steve Chiswell