[Radiance-general] Re: physically-based landscapes

[Peter Apian-Bennewitz]

Santiago Torres wrote:

>...
>
>Basically, as I understand, Carsten`s and Greg`s methods differ in that the
>first maps the image in a plane situated outside the window and the second
>(through an 'ad hoc' function) directly on the window plane. My question is
>this:
>
>- If one maps the image in a plane outside the window there will be some
>paralax error (though minimum) which can be reduced with distance
>  
>
>- And if the plane is on the window this should be noticeable
>- Or does it work like mkillum? would sun patches appear inside the room?
>- Or else: is there any way to map a HDR image in a source, something in the
>way skies are generated (maybe replacing the skyfunc?) and then use it as
>any other sky and/or ground? Somehow, for me this seems to be the most
>natural solution.
>
Mapping to a source works like mapping to a polygon, except that the
image u,v coordinates in the cal file depend on the view direction
vector Dx,Dy,Dz rather than on position coordinates Px,Py,Pz . The
formular depends on the type of lense used to take the image, either
fisheye (similar to an -vta image) or perspective wideangle.
With mapping to source, parallax error increases with nearby objects.
Specially when moving inside a room the outside looks a bit 'frozen' if
modelled as a source mapped image only. See
http://www.pab-opto.de/pers/animation/film2.html for an example of
source mapping and animation made in 1994.
Theoretical extra note: Imaging an image mapped to the window polygon
with u,v coordinates depending on position _/and_/ view direction. The
result would be indistinguishable from a 'real' view towards the
outside. Eh voila - that would be a 'lightfield' as used as core idea in
Greg's rholo.
In pratice,for architectural simulation of one building, map the far
surroundings (sky-line, etc) to the source, model the nearby buildings
as 'bricks' and map photos onto their faces. There's an 1999 example of
this at http://www.ise.fhg.de/alt-aber-aktiv/radiance/animation/ ,
though we had not pushed the idea as far as I would had liked, then.

>I hope all this makes any sense. 
>
it does. :-)

-Peter

-- 
 pab-opto, Freiburg, Germany, www.pab-opto.de