[OpenLayers-Users] The correct approach to using only Spherical Mercator projection maps

[christopher.schmidt at nokia.com]

On May 7, 2011, at 9:25 AM, ext Janis Elmeris wrote:

> Hello!
> 
> I am using an OpenLayers map with OpenStreetMap and Google map base layers. Currently I've get it working by setting map's projection to EPSG:900913, map's display projection to EPSG:4326, setting an option sphericalMercator=true for Google maps layer's and transforming OpenLayer.LonLat and OpenLayer.Geometry.Point from EPSG:4326 to EPSG:900913 every time I add one to the map. I've picked this up from various examples, so I'm not sure if this is the right approach in my situation. Is it?
> 
> If it is the right approach, I have several questions.
> 
> 1) Why should I set sphericalMercator=true for Google maps, but not for OpenStreetMap? Can the Google maps layers be also used with the option being false, and can OSM be used with the option true?

Google Layers can be used without that setting, in which case 
their coordinates are in geographic coordinates. However, this does not work with 
many features, like overlaying WMS layers and vector coordinates.

This option does not exist on the OSM layer. 

> 
> 2) What's the point of setting the map's projection to EPSG:900913 and map's display projection to EPSG:4326, if I still have to transform the coordinates every time my script interacts with the map (adding objects on specific coordinates)?

The displayProjection is designed to control the output of various
controls. At some point, automatic reprojection of points and vectors
may be built into OpenLayers, but because of the way the code works,
this is a complex change, which would likely result in an API 
change, and has not yet been implemented.

> 
> 3) Do I need the transformation at all, if I use only maps with the Spherical Mercator projection (Google maps and OSM are all supposed to be using Spherical Mercator)? Shouldn't everything already be in that projection?

You don't need any transformation if all coordinates are in projected 
meters, rather than in geographic coordinates. This is not usually
the situation.

Best Regards,
Christopher Schmidt

> 
> Thank you!
> Janis
> 
> 
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