In article <chr### [at] netplexaussieorg> , Christopher
James Huff <chr### [at] maccom>  wrote:

> Wouldn't it be much less confusing for the users if the function used
> scene-space coordinates instead of image-space?

But then it wouldn't be an image map any more:  The image simply can't know
where and how it is applied.  What you are suggesting sounds like uv-mapping
of some kind.

> file formats with a different coordinate system (< 0, 0> at the lower
> left, for instance) are modified to be oriented properly, couldn't the
> same be done for function images?

The current origin is *correct*.  Of any image the origin is at the upper left
corner and POV-Ray (tries) to make this true for all image formats (afaik only
TIFF allows other origins anyway).  If you check replace the function image by
a plain image map (or simply look at the source code) you will find that the
same is true for the function image.  The origin is that the upper left of the
image map that is being created.

Sure, the origin can be chosen arbitrarily, but for all computer images the
accepted standard (probably because that is where the beam usually starts on
CRTs) is to have the origin at the upper left rather than the lower left
commonly used in mathematics.

POV-Ray intentionally takes a middle way and "compensates" (see comment in
function 'map' in 'image.cpp') for this and places the image origin for an
image mapped "once" at <0,1,0>.  So as all other image types use the upper
left as origin together with this "compensation" it would be really illogical
to use the lower left for function images and thus not to compensate for it
just to allow Rune's special case exception.


    Thorsten

____________________________________________________
Thorsten Froehlich, Duisburg, Germany
e-mail: tho### [at] trfde

Visit POV-Ray on the web: http://mac.povray.org

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