[Geotiff] Re: How to add a projection to GeoTIFF?

[Frank Warmerdam]

Bruce Raup wrote:
> Hi Frank,
> 
> We at the US National Snow and Ice Data Center have a request to provide
> some of our data, which is in a global equal-area cylidrical projection,
> in GeoTIFF format.  However, one of our programmers here has found that
> GeoTIFF does not support equal-area cylidrical projections.  How can a
> projection be added to GeoTIFF?
> 
> Proj.4 supports equal-area cylidrical projections, so it seems like added
> it to GeoTIFF would simply be a matter of defining a new code for it and
> linking them together.  Is that right?
> 
> We are willing to do work in order to get this added, but we need some
> guidance on the process.  I've read the FAQ, and it appears that changes
> need to be proposed to some body.
> 
> Equal-area cylidrical is one of the standard projections within NASA's ECS
> (EOSDIS Core System), so we expect that we are not the only potential
> users of this projection with GeoTIFF.

Bruce (and other GeoTIFFers!),

I see you are correct, that there is no GeoTIFF code for equal-area
cylindrical, which I am more familiar with seeing referred to as Cylindrical
Equal Area.  I also see it still isn't listed in the projection methods in the
latest EPSG database.

I propose we add a new projection method code for it as:

   ValuePair(CT_CylindricalEqualArea, 28)

And that we use the parameters:

   CentralMeridian
   StdParallel1
   FalseEasting
   FalseNorthing

There is already a page for this projection on the GeoTIFF web site:

   http://www.remotesensing.org/geotiff/proj_list/cylindrical_equal_area.html

You asked about process for adding a new projection.  Since there isn't a
formal body doing specification revision, I normally just take it upon myself
to add new codes to libgeotiff and the geotiff web pages as they come up after
giving the members of the GeoTIFF mailing list a chance to comment.  So, to
that end, I am cc:ing this message to the GeoTIFF mailing list.  You might want
to subscribe in case any questions come up.

My only concern with adding this projection is that I am picking parameter
names somewhat arbitrariily based on the values in the web page linked above.
But I don't think those parameter names were really the result of careful
consideration.  Can you provide any documentation for the parameters?

In PROJ.4 I see the latitude is called the latitude of true scale or
standard parallel.

Best regards,
-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent