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

[Bruce Raup]

Frank et al.,

I'm wondering what the status of this issue is (adding Cylindrical
Equal-Area projection(s) to GeoTIFF).  Have we reached the finish line?
Is there anything more I can do to help finish the process?

Best regards,
Bruce

On 2004-07-16 16:12 -0600,  Bruce Raup wrote:

> 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/