Jose Gonçalves jagoncal at gmail.com
Tue Apr 1 13:00:27 EST 2014

```Hi

I suppose it should be PI/4 instead of PI/2.
That formula is an approximation of the exact Mercator projection for the
Hayford ellipsoid.
The differences in the Y coordinate are smaller than 10 meters, for
latitudes below 60 degrees. If that is ok for you you can go for the
ellipsoid projection::
+proj=intl +proj=merc

If you need more accuracy and your latitude extension is relatively small
you can adjust a scale factor and a false northing, and get a much better
accuracy.
This may avoid programming the formula.

Regards

José Gonçalves

2014-04-01 15:38 GMT+01:00 raul pra levis <raulfalco1978 at hotmail.com>:

> Hi Janne,
> thanks for the response.
> Our custom projection is an approximated Mercator Meter projection based
> on International 1909 ellipsoid.
> The approx formula is:
>
> y = ln ( tan(1/2 * atan(tan(lat_rad) /  1.0067642927) + PI/2) ) *
> 6378388.0
>
> The choice of using an approximated projection is historical and related
> by hardware limitations of thirty years ago.
>
> Regards,
>
> Raul
>
>
> > Date: Fri, 28 Mar 2014 21:52:28 +0200
> > From: support.mn at elisanet.fi
> > To: proj at lists.maptools.org
> > Subject: Re: [Proj] Add custom projection
>
> >
> > Hello,
> >
> > could you tell us why do you have a custom mercator
> > projection? and what is custom in it?
> >
> > Regards: Janne.
> >
> > ===========================================
> >
> > raul pra levis [raulfalco1978 at hotmail.com] kirjoitti:
> > >
> > >
> > >
> > > Hi,
> > > I work for a company where we have our custom mercator projection.
> > > I already developed code snippets to integrate such projection in
> proj4 4.8.0 (c++).
> > > Is there the chance to collaborate with develop team to integrate it
> in proj4 main trunk?
> > >
> > > Thanks and best regards,
> > >
> > > Raul Pra Levis
> > >
> > >
> > >
> > > _______________________________________________
> > > Proj mailing list
> > > Proj at lists.maptools.org
> > > http://lists.maptools.org/mailman/listinfo/proj
> >
> >
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>
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