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

[Janis Elmeris]

On 2011.05.07. 16:48, christopher.schmidt at nokia.com wrote:
> 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.

OK, so if OpenStreetMaps can be only sphericalMercator, this actually 
settles it (must use the option for Google), as I need OSM. (Not sure 
what WMS is meant for anyway, in the examples I've seen it looks like a 
fairly low resolution (rather an overview) of the world only.)

>> 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.

Thanks for the information! Is map's "projection" also used basically by 
the controls?

>> 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 Schmid

Thanks for the reply!
Janis

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