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

[Bruce Raup]

Frank,

We confirmed that the projection requires a central meridian and one
standard parallel.  When there's only one, is StdParallel1 the proper name?

For documentation, the Cylindrical Equal-Area projection is discussed in
Snyder, Map Projections -- a Working Manual (1987) on pg 76ff.

The GMT (Generic Mapping Tools (http://gmt.soest.hawaii.edu/))
documentation on the projection is at
http://gmt.soest.hawaii.edu/gmt4/doc/html/GMT_Docs/node84.html

Proj.4's "proj -lP" gives:

cea : Equal Area Cylindrical
        Cyl, Sph&Ell
        lat_ts=

So, except for the possibility of there being a different parameter name
when there is only one standard parallel, I think you have the parameters
correct.

Is there more I should do, or is it in your hands now?  Do you announce new
additions to the spec on this list?

Thanks,
Bruce

On 2004-07-16 13:50 -0400,  Frank Warmerdam wrote:

> 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,
>

-- 
Bruce Raup                                               Phone:  303-492-8814
National Snow and Ice Data Center, U. of Colorado, 449 UCB, Boulder, CO 80309
http://cires.colorado.edu/~braup/