Re: [OpenMap Users] Google Maps Projection

From: Tore Halset <halset_at_pvv.ntnu.no>
Date: Mon, 8 Mar 2010 23:27:55 +0100

Hello.

I am using OpenMap OgcWmsServlet with EPSG:900913 and it works just fine on top of Google Maps with clients like OpenLayers and route-me. There used to be a problem with portrait (dx<dy) images, but this was just fixed in svn trunk.

I agree that we should add the official EPSG-codes and I will make a patch for it to Don, but it is not needed to make overlay on top of Google Work.

Regards,
 - Tore.

On Mar 8, 2010, at 17:06, Christopher Mueller wrote:

> All,
>
> I have successfully implemented a WMS provider that utilizes openmap to render the images from various datasets. However, I am running into a problem projecting the image into the "Google Projection" (EPSG:900913). I have tried using the built in "CoordinateReferenceSystem.getCode("EPSG:900913")" to generate the needed GeoProj object, but it appears to be exactly the same as the "normal" Mercator projection. The images produced when using the two projections are identical.
>
> After some digging, I found the following resources, all of which allude to the "trick" being "nulling the nadgrid" - which essentially means NOT applying the WGS84 shift after translating from Meters.
>
> http://docs.codehaus.org/display/GEOTDOC/Google+Maps+Projection
> http://crschmidt.net/blog/archives/238/understanding-googles-projection-slightly-anyway/
> http://www.sharpgis.net/post/2008/05/SphericalWeb-Mercator-EPSG-code-3785.aspx
>
> The last link also indicates that the EPSG governing body has officially added the "Spherical Mercator / Web Mercator" projection to it's database - EPSG: 3785.
>
> So there seems to be enough information to replicate the projection properly - the issue is, I can't seem to find the right hook to get the projection correct in openmap.
>
> Has anyone out there successfully made the "Google Projection" work in openmap??
>
> Thanks in advance for any help,
>
> Best,
>
> Chris
>
>
> --
> Christopher Mueller | Scientific Developer
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Received on Mon Mar 08 2010 - 18:10:47 EST

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