[OpenLayers-Dev] Map Rotation

Stephen Woodbridge woodbri at swoodbridge.com
Sat Dec 19 00:12:02 EST 2009

Well, I would differ to any of the OL devs, but here is my 2 cents.

I am thinking that the fundamental problem is the OL needs to make 
requests for an image and the request needs to be able to be interpreted 
by mapserver or whomever is serving the image. So if you pan to the 
right you need to make sure that the coordinated of the view in your 
request to mapserver return the appropriate image that you would expect 
after the pan. This would be true as well for zooms, and any other OL 
interactions like mouse position controls and such.

One idea might be to define a projection that in effect does the 
appropriate rotation that mapserver is applying. But I'm not sure how 
the requests should be make to mapserver since (see note below) you can 
not use the CGI interface is the docs are correct. My guess is that you 
would have to write a new OpenLayers.Layer.Mapserver.Rotated class the 
understands how to appropriately make the requests to mapserver. And 
probably have to write a mapscript handler to receive the requests and 
generate the image.

Also read the fine print on the MAP ANGLE parameter. I believe it says 
that only works with mapscript and NOT the CGI interface.

-Steve W

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?
> *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.

More information about the Dev mailing list