raytracing, here's a link to an engraving describing this very, very early 

on the Art of Measurement).
http://www.columbia.edu/cu/lweb/eresources/exhibitions/treasures/html/55.html
This page doesn't explain much in English, but I have a translation in a 
book (that I don't have here right now). IIRC, the string is attached from 
the painted object to the wall, and the intersections between the string and 
the screen are recorded on paper, forming a shape that the artist uses as 
basis for the final painting or drawing. I don't remember exactly how the 
"pixel" is recorded, but I think it's by using some sort of cross-hair 
device attached to the frame (what the guy on the right is doing). I'll 
check later.

And yes, it took time ;)

G.

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"Gilles Tran" <tra### [at] inapgfr> wrote:

> raytracing, here's a link to an engraving describing this very, very early

> on the Art of Measurement).
> http://www.columbia.edu/cu/lweb/eresources/exhibitions/treasures/html/55.html

You put me in my place :-) [Big cheesy grin]
I saw that illustration years ago and I thought he was inventing the double
base :-)

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Gilles Tran wrote:

> raytracing, here's a link to an engraving describing this very, very early 

> on the Art of Measurement).
> http://www.columbia.edu/cu/lweb/eresources/exhibitions/treasures/html/55.html
> This page doesn't explain much in English, but I have a translation in a 
> book (that I don't have here right now). IIRC, the string is attached from 
> the painted object to the wall, and the intersections between the string and 
> the screen are recorded on paper, forming a shape that the artist uses as 
> basis for the final painting or drawing. I don't remember exactly how the 
> "pixel" is recorded, but I think it's by using some sort of cross-hair 
> device attached to the frame (what the guy on the right is doing). I'll 
> check later.

Note this is more 'scanline rendering' than raytracing.  For raytracing 
you would position the 'string' to one pixel of the 'image' after the 
other and look into the 'scene' where it points at.  Here the string is 
positioned in the scene and from there you look where it intersects the 
image.  An actual 'scanlining' of course does not take place.

Still a nice examle of 'early CG'.

BTW there is a true early raytracing example (although quite 
unspectacular) in the work of Leonardo da Vinci:

http://www-public.tu-bs.de:8080/%7Ey0013390/files/leonardo.png

(excuse the bad quality - photographed from the paperback version of "La 
scoperta dell'ombra" - the discovery of the shadow by Roberto Casati)

It illustrates that shadows comply with the rules of ray optics and that 
by mentally substituting the light source and the eye/camera you can 
simplify a lot of things (which is the essence of raytracing).

Christoph

-- 
POV-Ray tutorials, include files, Sim-POV,
HCR-Edit and more: http://www.tu-bs.de/~y0013390/
Last updated 27 Feb. 2005 _____./\/^>_*_<^\/\.______

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"Gilles Tran" <tra### [at] inapgfr> wrote:
> I don't remember exactly how the
> "pixel" is recorded, but I think it's by using some sort of cross-hair
> device attached to the frame (what the guy on the right is doing). I'll
> check later.
>
> And yes, it took time ;)
>
> G.

In the open frame there are two cross-wires, one horizontal which move up
and down and the vertical one can move left-right/right-left. They are used
to coincide with the string. Then the string is released and the paper (or
canvas or wood plank etc) is turned back to the frame, and the point is
marked with a pencil. Repeat that until the image (made of points) is
accurate enough.
very,very long process... that's why they are 2 guys on the print, "Albrecht
Durer and Associated" ;-)


Rene
http://rene.bui.free.fr - online portfolio

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d57nnr$hr5$1@chho.imagico.de...
> Note this is more 'scanline rendering' than raytracing.  For raytracing 
> you would position the 'string' to one pixel of the 'image' after the 
> other and look into the 'scene' where it points at.  Here the string is 
> positioned in the scene and from there you look where it intersects the 
> image.

Well, given the technology shown here, it couldn't be "raytracing" stricto 
sensu obviously. The interesting thing is that these people were already 
creating pictures using analog rays instead of digital ones.

I couldn't find my book but here's a more detailed explanation:
http://www.vam.ac.uk/images/5166-popup.html

"A pointer is attached to a thread running through a pulley on the wall. The 
thread represents a ray of light passing through the picture plane to the 
theoretical eye-point denoted by the pulley. As one man fixes key points on 
the lute, his assistant records the vertical and horizontal co-ordinates of 
the thread as it passes through the frame, and plots each new point to 
create a drawing. The principle is correct, but the procedure is complicated 
and rarely produced good results. "


G.

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On Tue, 03 May 2005 13:36:26 +0200, Christoph Hormann <chr### [at] gmxde>
wrote:

>Still a nice examle of 'early CG'.

Not a CG but still art ...

Ancient obelisks were considered as sacred to the sun god, representing the
sunrays embodied in stone.

And according to some resources Coptic word "pyramid" meant "sun's ray" and
pyramid's shape reflects cone of rays.

ABX

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Among other things, Gilles Tran saw fit to write:


> raytracing, here's a link to an engraving describing this very, very early

> on the Art of Measurement).
>
http://www.columbia.edu/cu/lweb/eresources/exhibitions/treasures/html/55.html

Maybe I've missed something, but I've found this:
http://www.frontiernet.net/~eugene.ressler/
(see section 4.1 of the manual (page 28 in the pdf))

-- 
light_source{9+9*x,1}camera{orthographic look_at(1-y)/4angle 30location
9/4-z*4}light_source{-9*z,1}union{box{.9-z.1+x clipped_by{plane{2+y-4*x
0}}}box{z-y-.1.1+z}box{-.1.1+x}box{.1z-.1}pigment{rgb<.8.2,1>}}//Jellby

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