[MetaCRS] Translation WGS84 to Mercator

[Mikael Rittri]

Hello Gleb,

According to http://spatialreference.org/ref/epsg/3395/proj4js , the 
definition of EPSG:3395 (WGS84 / World Mercator) in proj4js is 

+proj=merc +lon_0=0 +k=1 +x_0=0 +y_0=0 +ellps=WGS84 +datum=WGS84 +units=m +no_defs 

If you instead use

+proj=merc +lon_0=90 +k=1 +x_0=10018754.171395 +y_0=0 +ellps=WGS84 +datum=WGS84 +units=m +no_defs

you should get a Mercator with projected coordinates that are centered on longitude 90E, 
so they are interrupted along the meridan 90W, far from Russia, instead of meridian 180E.  

The value for x_0 is a quarter of the WGS84 equator in meters, which is the easting value for 
meridian 90E in EPSG:3395.  This means that the coordinates in this recentered projection
agree with EPSG:3395 from 90W and east to 180E.  (But between 180E and further east 
to 90W, the eastings are 40075016.685578 m larger, which is what you need to get continuity 
over meridian 180E.)

I haven't tested this behaviour with proj4js, but it works with the Proj.4 of FWTools:

>proj +proj=merc +lon_0=90 +k=1 +x_0=10018754.171395 +y_0=0 +ellps=WGS84 +datum=WGS84 +units=m +no_defs
190 0
21150703.25     0.00

Best regards,
Mikael Rittri
Carmenta
Sweden
http://www.carmenta.com

-----Original Message-----
From: metacrs-bounces at lists.osgeo.org [mailto:metacrs-bounces at lists.osgeo.org] On Behalf Of Kosolapov Gleb
Sent: den 23 november 2010 09:55
To: metacrs at lists.osgeo.org
Subject: [MetaCRS] Translation WGS84 to Mercator

Hi, everyone from Russia!

I'm using proj4js with OpenLaerys. 
I must translate WGS84 to Mercator (EPSG:3395, for example).
My country lies through 180th meridian (antimeridian). So, in WGS84 this territory ends near 190 longitude. And everything works fine.
But when I transform 190 lat to Mercator, I get negative value -18924313.434856504. That's very bad for every operation with Mercator coordinates in OpenLayers.

Please, help me how to transform 190 lat to positive Mercator using proj4js...

Regards, Gleb.
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