<div dir="ltr"><div><div><div><div><div>Hi<br><br></div>I suppose it should be PI/4 instead of PI/2.<br></div>That formula is an approximation of the exact Mercator projection for the Hayford ellipsoid.<br></div>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::<br>
</div>+proj=intl +proj=merc<br><br></div><div>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.<br></div><div>This may avoid programming the formula.<br>
<br></div><div>Regards<br><br></div><div>José Gonçalves<br><br></div><div><br></div><div><br></div></div><div class="gmail_extra"><br><br><div class="gmail_quote">2014-04-01 15:38 GMT+01:00 raul pra levis <span dir="ltr"><<a href="mailto:raulfalco1978@hotmail.com" target="_blank">raulfalco1978@hotmail.com</a>></span>:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div><div dir="ltr">Hi Janne,<br>thanks for the response.<br>Our custom projection is an approximated Mercator Meter projection based on International 1909 ellipsoid.<br>The approx formula is:<br><br>
<p class="MsoNormal" style="margin-top:0cm;margin-right:0cm;margin-bottom:6.0pt;margin-left:5.0cm"><font face="Times New Roman"><span><span style="font-size:12pt">y
= ln ( tan(1/2 * atan(tan(lat_rad) /<span>
</span>1.0067642927) + PI/2) ) * 6378388.0</span></span></font></p>
<br>The choice of using an approximated projection is historical and related by hardware limitations of thirty years ago.<br><br>Regards,<br><br>Raul<br><br><br><div>> Date: Fri, 28 Mar 2014 21:52:28 +0200<br>> From: <a href="mailto:support.mn@elisanet.fi" target="_blank">support.mn@elisanet.fi</a><br>
> To: <a href="mailto:proj@lists.maptools.org" target="_blank">proj@lists.maptools.org</a><br>> Subject: Re: [Proj] Add custom projection<div><div class="h5"><br>> <br>> Hello,<br>> <br>> could you tell us why do you have a custom mercator<br>
> projection? and what is custom in it?<br>> <br>> Regards: Janne.<br>> <br>> ===========================================<br>> <br>> raul pra levis [<a href="mailto:raulfalco1978@hotmail.com" target="_blank">raulfalco1978@hotmail.com</a>] kirjoitti: <br>
> > <br>> > <br>> > <br>> > Hi,<br>> > I work for a company where we have our custom mercator projection.<br>> > I already developed code snippets to integrate such projection in proj4 4.8.0 (c++).<br>
> > Is there the chance to collaborate with develop team to integrate it in proj4 main trunk? <br>> > <br>> > Thanks and best regards,<br>> > <br>> > Raul Pra Levis<br>> > <br>> > <br>
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