[OpenLayers-Dev] Map Rotation

Andreas Hocevar ahocevar at opengeo.org
Sun Dec 20 17:18:38 EST 2009

Alexei Peters wrote:
> So, if using GeoServer, does the ANGLE parameter apply to all features 
> (WFS, WMS, tilecaches, etc..)? 
> Also, you mention that OL has to know how to handle the rotation.  I 
> don't think there's a setting for this now, though, right?
> Is there anyone on the OL team that's thinking about how to handle this?

As Chris already said, you cannot do this in OpenLayers. For this to 
work, OpenLayer would need to support axis rotation. For vector layers, 
implementing it would be doable. But all image maps rely on a grid of 
div elements that you cannot rotate, so that would be much harder. You 
would have to render tiles onto a canvas instead of div elements.

Having said that, making OpenLayers support axis rotation would be a 
challenging task, which would require a lot of funding, and would make 
more sense for a next generation of OpenLayers than for 2.x.


> ------------------------------------------------------------------------
> *From:* Andrea Aime [mailto:aaime at opengeo.org]
> *Sent:* Fri 12/18/2009 2:38 AM
> *To:* Stephen Woodbridge
> *Cc:* Christopher Schmidt; Alexei Peters; dev at openlayers.org
> *Subject:* Re: [OpenLayers-Dev] Map Rotation
> Stephen Woodbridge ha scritto:
> > 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.
> In GeoServer land we're about to add the same parameter.
> However, once you rotate the map OL has to know and handle the rotation
> otherwise panning and zooming go bye bye...
> Cheers
> Andrea
> --
> Andrea Aime
> OpenGeo - http://opengeo.org <http://opengeo.org/>
> Expert service straight from the developers.
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Andreas Hocevar
OpenGeo - http://opengeo.org/
Expert service straight from the developers.

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