Re: Map Projections

• To: Doug Lindholm <lind@xxxxxxxx>
• Subject: Re: Map Projections
• From: Bill Hibbard <hibbard@xxxxxxxxxxxxxxxxx>
• Date: Thu, 15 Feb 2001 16:37:27 -0600

Hi Doug,

> Could someone steer me in the right direction here? I have a terrain
> data set that looks like:
> 
>    (lon, lat) --> alt
> 
> I have a lovely 2D image by mapping lon -> XAxis, lat -> YAxis, and alt
> -> RGB. How would I go about displaying this with a Lambert conformal
> projection?
> 
> Should I use visad.data.hdfeos.LambertConformalConic for the
> CoordinateSystem?
> 
> I'll have multiple Data objects that are functions of (lon, lat) and I'd
> rather not have to define them with a special CoordinateSystem. (I've
> been looking at Test11 which does this for PolarCoordinateSystem.)  I'd
> like to be able to change projections by changing a property of my
> Display, not my Data.

I'll describe the general approach, and then I'm sure Steve
Emmerson or Don Murray from Unidata will talk about their
work actually doing this in their Metapps system.

What you do is construct three new DisplayRealTypes for
a new display side coordinate system. They would all have
single = true and in other ways be similar to what you
see for:

 (Display.Latitude, Display.Longitude, Display.Radius)

You might call them LambertLat, LambertLon and LambertZAxis.
Then you define a CoordinateSystem extension that defines
the invertible transform between them and (XAxis, YAxis, ZAxis)
where LambertZAxis is always equal to ZAxis. XAxis and YAxis
play the role of map coordinates in the Lambert projection.

Then define an instance of your new CoordinateSystem with
reference (XAxis, YAxis, ZAxis).

Then define a DisplayTupleType for
(Display.Latitude, Display.Longitude, Display.Radius) with
the new CoordinateSystem instance.

Now construct ScalarMaps:

  Latitude -> LambertLat
  Longitude -> LambertLon

and you're in business.

Like I say, Don and Steve can fill you in on the details
and probably show you where everything you need is already
done in MetApps.

Cheers,
Bill
----------------------------------------------------------
Bill Hibbard, SSEC, 1225 W. Dayton St., Madison, WI  53706
hibbard@xxxxxxxxxxxxxxxxx  608-263-4427  fax: 608-263-6738
http://www.ssec.wisc.edu/~billh/vis.html

• Follow-Ups:
  • Re: Map Projections
    • From: Don Murray

• References:
  • Map Projections
    • From: Doug Lindholm