[Proj] A template for documenting projections

Kristian Evers kreve at sdfe.dk
Thu Sep 8 18:04:22 EST 2016

I think the generic parameters like false easting/northing should be documented elsewhere. 
In fact they already are on http://proj4.org/parameters.html although that page could use some more work.

Yes, you are absolutely right about the +k_0 and +lat_ts options!

Fra: Even Rouault [even.rouault at spatialys.com]
Sendt: 9. september 2016 00:32
Til: proj at lists.maptools.org
Cc: Kristian Evers
Emne: Re: [Proj] A template for documenting projections

Le jeudi 08 septembre 2016 23:50:09, Kristian Evers a écrit :
> All,
> I have spend a few hours documenting the Mercator projection in the hopes
> that it can serve as a template for the rest of the projections that still
> need to be documented.
> http://proj4.org/projections/merc.html
> This is just my first initial thoughts on how to document a projection.
> I've divided the page into a few sections:
> - A short introduction
> - A table with a few key facts
> - Plot(s)
> - Usage/examples
> - Underlying math
> - References
> I would like to hear your thought on this. Is this a sufficient level of
> documentation? Did I leave out something obvious (in general terms, not
> specific to the Mercator projection)? Do you like the general format?


Looks good !

What about documenting the false easting x_0, false northing y_0 parameters ?
But as those ones apply for all projections since they are applied in the
generic code of pj_fwd/pj_inv, they should perhaps be documented in a general
page. The same applies for the central meridian (lon_0).

Regarding Mercator, proj actually supports 2 forms, the one with +lat_ts
(Mercator_2SP) and the one with the scale factor +k_0 (Mercator_1SP)
I found this with libgeotiff projection catalog, which might be a useful
resource (the original URL is defunct since a few days, hence this wayback
machine URL) :


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