Re: Some questions regarding transformations in SVG

On Sun, Nov 16, 2014 at 10:52 PM, Juergen Roethig <roethig@dhbw-karlsruhe.de
> wrote:

> Rik Cabanier wrote:
>
>
>>
>> On Sun, Nov 16, 2014 at 12:43 AM, Juergen Roethig <
>> roethig@dhbw-karlsruhe.de <mailto:roethig@dhbw-karlsruhe.de>> wrote:
>>
>>     Steve Schafer wrote:
>>
>>         On Sat, 15 Nov 2014 19:37:35 +0100, you wrote:
>>
>>             You really want to tell me that the SVG WG does not even
>>             want to consider non-affine transformations for SVG because
>>             it might take more computational power than "simple matrix
>>             math"?
>>
>>
>>         Not just more computational power, but more expressive power.
>>         The space
>>         of "non-affine transformations" is effectively infinite. Are you
>>         willing
>>         to limit that to some subset (e.g., projective geometry)? Or do
>>         you want
>>         everything? The more you encompass, the more your means of
>>         expressing a
>>         transformation begins to look like a general-purpose programming
>>         language. There's no point in reinventing JavaScript within
>>         SVG--it's
>>         already there.
>>
>>
>>     I do not want "everything" out of "infinity", for sure! If
>>     transformations other than affine ones had been discussed before in
>>     the SVG WG, coming to some sort of conclusion, I will see what to
>>     make out of it. Unfortunately, the specs (the existing 1.1 as well
>>     as the upcoming 2) as well as my Google search on the topic
>>     (probably using the wrong keywords) don't reflect such a discussion.
>>     That's why I ask what might have been discussed before!
>>
>>
>> Can you give an example of what such non-affine transformations look
>> like? Do you know of any tools that offer them?
>>
>>     Of course, "projective geometry" might be a candidate for such a
>>     class of transformations, especially with regard to the z-index
>>     which hopefully makes it in SVG2!
>>
>>
>> I don't understand why z-index is special. Can you eleborate?
>>
>
> An example of such a non-affine transformation might be the one-point
> perspective (http://en.wikipedia.org/wiki/Perspective_projection#One-
> point_perspective). This is some sort of projection of a point in a
> three-dimensional coordinate system to a point in a two-dimensional
> coordinate system (i.e. a plane). Why I would need z-index is obvious ...
> although I know that z-index in SVG2 is currently defined as an index just
> controlling the rendering order, it might also be regarded as the third
> (missing) dimension, although with somewhat restricted accuracy (since it
> is an integer value).
>

I didn't hear anyone propose to repurpose z-index as an actual dimension.
You will find a lot of resistance to change this common HTML/CSS property.


> Other examples of non-affine transformations are all sorts of map
> projections (http://en.wikipedia.org/wiki/Map_projection) which neither
> need a third dimesion (the z-index) nor are probably among the first
> candidates for transformations to be implemented in SVG since they might be
> somewhat too special.
>

If you could do this with excellent performance using a JS libary, would
that be acceptable?


> Tools supporting such transformations/projections? The former should be
> supported by all sort of tools which allow perspective views of
> three-dimensional (virtual) worlds, and the latter might be a case of
> special cartographic tools.


Can you give an example? I'm not familiar with any of such tools and would
like to see how they work.
It's likely that I'm not the only one.