RenderMan & RISpec, Modeling slabs

Hi, I am trying to model a thin slab of material (the RIB is below). My
approach is use a cube of scaled (7.5, 10, 0.1) bilinear patchs. The
camera is looking at the center of one of the slab faces (XY plane).
Inside the slab shader I am printing the shading point P. I noticed
that I am getting repeated points differing only in z-coordinate: i.e.
P: [-2.812 4.792 17.950] and P: [-2.812 4.792 18.050], for example.

My question is if that is normal (maybe is the way Renderman works) or
I am having a problem with normals.

BTW if anyone knows where I can download models, I would appreciate. I
have looked in the Stanford and the Aim-at-Shape repositories. I am
interested something thin, like a sheet of paper.

========= RIB =========

version 3.03
Display "slab.tif" "file" "rgba"
Format 400 300 1

# Aliasing
ShadingRate 1
PixelSamples 8 8
PixelFilter "sinc" 4 4
Hider "hidden" "jitter" [0]

Projection "perspective" "fov" 45

# Camera
# Look From: 0 5 18
# Look At: 0 5 0
Rotate 180 0 1 0
Translate -0 -5 -18

WorldBegin

LightSource "ambientlight" 0 "intensity" [0.3] "lightcolor" [1 1 1]

# Front spotlight
LightSource "spotlight" 1
"lightcolor" [1 1 1]
"intensity" [60]
"from" [0 6 15] "to" [0 6 0]
"float coneangle" [0.15]
"string ShadowMapName" ["paper_shadow_front.tdl"]
"string NormalMapName" ["paper_normal_front.tdl"]

# Vertical plane
AttributeBegin
TransformBegin
Translate 0 5 0
Scale 7.5 10 0.1

Surface "mySurface"

SolidBegin "primitive"
TransformBegin
Scale 1 1 1
Patch "bilinear" "P" [0.5 0.5 0.5 0.5 0.5 -0.5 0.5 -0.5 0.5 0.5 -0.5
-0.5]
Rotate 90 0 0 1
Patch "bilinear" "P" [0.5 0.5 0.5 0.5 0.5 -0.5 0.5 -0.5 0.5 0.5 -0.5
-0.5]
Rotate 90 0 0 1
Patch "bilinear" "P" [0.5 0.5 0.5 0.5 0.5 -0.5 0.5 -0.5 0.5 0.5 -0.5
-0.5]
Rotate 90 0 0 1
Patch "bilinear" "P" [0.5 0.5 0.5 0.5 0.5 -0.5 0.5 -0.5 0.5 0.5 -0.5
-0.5]
Rotate 90 0 1 0
Patch "bilinear" "P" [0.5 0.5 0.5 0.5 0.5 -0.5 0.5 -0.5 0.5 0.5 -0.5
-0.5]
Rotate 180 0 1 0
Patch "bilinear" "P" [0.5 0.5 0.5 0.5 0.5 -0.5 0.5 -0.5 0.5 0.5 -0.5
-0.5]
TransformEnd
SolidEnd

TransformEnd
AttributeEnd

WorldEnd

Hello,

A possible explanation is that you are using a renderer that shades in
SIMD (such as 3delight, prman or renderdotc). This means that it prints
"P" for an entire grid at once. So each row of a grid will have
effectively only one changing coordinate (in your case 'Z' for the
sides of the slab).

- Aghiles
www.3delight.com

Hello,

A possible explanation is that you are using a renderer that shades in
SIMD (such as 3delight, prman or renderdotc). This means that it prints
"P" for an entire grid at once. So each row of a grid will have
effectively only one changing coordinate (in your case 'Z' for the
sides of the slab).

- Aghiles
www.3delight.com

Thanks Aghiles, in fact I am using 3delight. Then, what happen with a
middle point? e.g. P: [-2.812 4.792 18.0]?