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Re: ucar.unidata.geoloc.projection.* questions

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  • Subject: Re: ucar.unidata.geoloc.projection.* questions
  • Date: Fri, 07 Apr 2006 12:33:46 -0600


Tom Margolis wrote:

John,
I am a software developer with UCAR working on 4DWX projects. We are using the ucar.unidata.geoloc.projection.* package for converting projected data to lon/lat values. I have some questions about this package - the first burning question is: how do these projection classes (e.g. LambertAzimuthalEqualArea) handle rotation and translation? I don't see any means to do so. Or is there another package/suite of classes that the unidata libraries use to handle translated/rotated projection data? 

Thanks much,

Tom Margolis
The projection functions are pretty standard, taken from Snyder. 
They should have false_easting, false_northing parameters (translations) 
although only a few actually do, because we havent seen any grids that use it. 
these are easy enough to add, by simply adding or subtracting from the 
projection coordinate before calling the projection. Weve been planning on 
adding those.
I'm not familiar with the rotation issue. Is it a rotation of the projection plane? If so, then you could again preprocess the coordinates from the rotated cordinates to the ones needed by the projection routine. 
The usual thing would be to do both a rotation and translation with a 3x3 
matrix, aka an affine transformation.