In article <3caf30b1@news.povray.org>,
 "Thorsten Froehlich" <tho### [at] trfde> wrote:

> 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.

I'm not talking about the mapping applied to the image. I'm just saying 
that people aren't going to think in the internal POV-Ray image 
coordinate system when writing a function that may or may not be used in 
an image, and they shouldn't have to.


> 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.

Actually, that is just an arbitrary choice. Most image formats work that 
way, but you can't make the assumption all do. There are several other 
formats besides TIFF that use different systems (I think SGI RGB is 
one), and some popular API's (OpenGL for example) use the lower left 
corner as the origin.

POV should compensate for the fact that a function's origin is at < 0, 
0, 0>, and not < 0, 1, 0>, as most image file formats have it. The 
internal coordinate system of the image should be hidden from the user. 
All they should have to care about is where the "top left" and "bottom 
right" map to in the scene coordinate system. Exposing it in this way is 
inconsistent, counter-intuitive and very user-unfriendly.

-- 
Christopher James Huff <chr### [at] maccom>
POV-Ray TAG e-mail: chr### [at] tagpovrayorg
TAG web site: http://tag.povray.org/

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