Hi Garrett-
"Campbell, Garrett" wrote:
>
> I am attempting to use the mcidas meteosat navigation module
>
> The documentation is obscure.
The best source for documentation is the McIDAS programmer's
reference which documents the MSAT nav module. There is a link
from the javadocs for MSATnav.
> 1. Sometimes Mcidas lists longitude positive to the west.
The convention in VisAD is positive east longitude which is
opposite of McIDAS and VisAD. The *nav routines are java
conversions of the McIDAS FORTRAN nav modules. Since the
McIDAS transformations use positive west longitude, all
incoming longitudes are multiplied by -1 before the transforms
are done.
> 2. line and elemement numbers are interchangable in some sence since the
> Meteosat 7
> satellite is at 0 longitude.
I don't think this is true. The line/element numbers refer
to the file (AREA) coordinates.
> 3. Line numbers could count from south to north or north to south.
> Similarly element
> numbers could count either increasing to the west (as the
> satellite scans) or
> increasing to the east (as a picture would show).
In MSATnav, area ele/lin (0,0) is the first pixel in the (upperleft)
corner of the image which I believe is the McIDAS convention.
AREACoordinateSystem has 0,0 in the lower left and sets the
flipped line coordinates flag in the nav module.
> Has anyone used edu.wisc.ssec.mcidas.MSATnav?
Yes, through AREACoordinateSystem.
> What convention do you use for latitude and longitude/ line and element
> in the routines calls to toLatLon and toLinEle.
the default transforms are (element, line) <-> (Latitude, Longitude).
Longitude is in degrees East. line and element are
in file (AREA) coordinates not image coordinates. You can transform
from file to image coordinates using the imageCoordToAreaCoord
and areaCoordToImageCoord methods.
I did the conversion from McIDAS FORTRAN to VisAD Java, so
if you have a specific question, let me know. The code in
the toLinEle and toLatLon methods is as well documented as
the corresponding FORTRAN code (which is pretty much
non-existant).
Don
*************************************************************
Don Murray UCAR Unidata Program
dmurray@xxxxxxxxxxxxxxxx P.O. Box 3000
(303) 497-8628 Boulder, CO 80307
http://www.unidata.ucar.edu/staff/donm
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