[Mapserver-dev] Rotated Map Rendering

[Sean Gillies]

On May 20, 2004, at 7:06 AM, Stephen Woodbridge wrote:

> OK, I hate to jump into a thread late and into one that I have only 
> half been following, but what the hey:
>
> The view model that I have always worked with in the CAD/CAM and 
> graphics world is the standard camera model i.e.: world space -> 
> projected space -> to clipped 2d space -> viewport space or device 
> coordinates. OK so I know we are not trying to redesign the mapserver 
> viewing pipeline.
>
> So I liked the idea that someone suggested about an output frame or 
> view port definition that would describe a final transformation of the 
> image. I was thinking that this could be defined to cause a simple 
> image transform as the image is output. For now only allow ROTATION in 
> increments of +-90 degrees. and this would be handled just before the 
> OUTPUTFORMAT processor is invoked. May be like
>
> OUTPUTFORMAT
>   ROTATEOUTPUT 90
>   ...
> END
>
> ALSO, If this is set then image.x and image.y are transformed on input 
> so they align correctly with the internal image. If other parameters 
> need to be adjusted to them at the same time. This keeps mapserver 
> pretty much insulated from any of these changes.
>
> By limiting the transforms to +-90 degrees increments the transform 
> becomes one of just swapping x/y values and/or min/max values which 
> should be fast and the same for pixel outputs.
>
> So I probably have missed the whole point of this discussion and this 
> is just extraneous noise so feel free to ignore it if it doesn't 
> apply.
>
> -Steve W.
>

Steve W., thanks for mentioning the camera model, that's what I was 
trying to
describe in my previous email.  Conceptual and programmatic separation
between the map and the view model would be a good thing.  For example, 
in
the real world when you take a map and rotate it -- it is the exact same
map, still pointing north (in most common cases) -- only the the view of
it has changed.  If we add rotation to the mapObj itself, we add 
complexity
and make it less like a real-world object.  This could make it harder 
for
users to understand.

I think that the WEB element is a more natural spot for the rotation 
stuff
than the OUTPUTFORMAT.  We are already keeping view model-ish and
application-specific parameters like MAXSCALE there.

Sean

--
Sean Gillies
sgillies at frii dot com
http://users.frii.com/sgillies