[OpenLayers-Dev] Map Rotation

Stephen Woodbridge woodbri at swoodbridge.com
Thu Dec 17 22:27:57 EST 2009

Christopher Schmidt wrote:
> On Thu, Dec 17, 2009 at 02:39:41PM -0800, Alexei Peters wrote:
>> Hi Everyone,
>> I currently work for a small GIS consulting firm and one of the projects we're currently working on has a potential requirement for rotating the map (so north doesn't point up, but rather to the right for example).
>> Has anyone any idea of how to do this, or has done this?  My company would be even willing to fund this effort if need be.
>> I'd love to hear anyone's thoughts on this.
>  1. In Javascript/Images/DOM (ignoring Canvas for the moment), there is 
>     no way to make an image exist on an angle.
>  2. Canvas has some support for this, I believe, but is limited in where
>     you can use it.
> Generally speaking, what you would do to solve this problem would be to
> pre-rotate your map (in a tool like photoshop, or something equally non
> OpenLayers related), and then work with at that point. Some people on
> the list have had some experience with that way of using OpenLayers; a 
> key aspect of this would be to write a translation from your map coordinates
> (which will likely be in pixels after the rotation) to geogrpahic coordinates,
> but that's not too hard, in general.
> Best Regards,

If you are using mapserver I believe there has been some work that would 
allow the image to draw with north rotated say to the east. Look for the 
ANGLE parameter in the MAP object.

-Steve W

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