[Radiance-general] Re: projection plane

[Greg Ward]

> From: Qing Xu <qingxu@itc.it>
> Date: Tue Oct 22, 2002  6:41:54 AM US/Pacific
>
> For this moment, I want to know the position of project plane in the
> context of
> perspective projection. I looked for inside the codes, but I did not
> find. Where can I find that in source codes? Actually, we want to
> simulate the effect for changing the focus distance with the fixed view
> point. How to do that? Is the view point the perspective projection
> center in Radiance? What is the real meaning for focus distance in
> Radiance?

The Radiance image projection code is in "ray/src/common/image.c".  A 
guide to the source tree may be found on the website under "Documents":

	http://radsite.lbl.gov/radiance/refer/index.html

The "view center" as it's often called does not really exist in 
Radiance per se.  In fact, one could argue that there is no such thing 
for a pinhole camera, which is what rpict simulates.  In order to have 
depth of field, you have to have a sampled aperture and a focus 
distance, neither of which are present in the default Radiance view 
model.  Instead, you give rpict a view origin (-vp Ox Oy Oz) and 
direction vector (-vd Dx Dy Dz), which says where the camera is looking 
from and the direction it is looking in.

To get motion blur, you need to sample over an aperature with a 
particular view center, and I wrote a script called "pdfblur" that does 
just this.  You can pass the views produced by pdfblur to rpict or 
(preferably) pinterp to get a depth-of-field blurred image.  See the 
pdfblur(1) man page for details.  I will send you an example image 
generated with pdfblur and pinterp.

-Greg