CS348b2007

Project Proposal : Sakura ("Cherry Blossom")

Team

Images

Overview

3D L-System

Background

Tree Rendering

http://www.nbb.cornell.edu/neurobio/land/OldStudentProjects/cs490-94to95/hwchen/pp1.gif

Tree Design Evolution

Basic Texture, No Branching

Basic Branching, Lighting

Model Leaves, Perspective

True Branching, Cherry Tree Properties

Gnarled Rotations, Proportional Trunk

Smooth Gnarled, Reduce Leaf Noise

SpeedTree Implementation (for reference)

Procedural Bark

Texture Generation

0307-sakurabark-1200

Texture Mapping

Classic Plane Curves

Background

Prunus serrulata are dicots and posses five petals, five sepals, several stamen and a pistil.

We observed that in this case that the beauty of nature coincides with the beauty of mathematics. More specifically, the shape and geometry of these blossoms can be recreated with curves defined in polar coordinates.

Blossom Rendering

We will choose curves that most closely resemble the shapes of most importantly the petals and sepals. Here is a diagram of the parts of a typical dicot:

What currently looks like the best choices are the cardioid

or the 5 petal rose curve for the petals

and the 5 point hypercycloid for the sepals.

All petals together:

and then with varied sine and cosine noise added to the z-component as well as variance in heights:

The petals are cardioids with the z-coordinate following the shape of a paraboloid to create the upcurving effect of the petals. The position of the petals around the center of the blossom are calculated according to those of the 5 petal rose curve.

In addition we will use sin/cosine curves with noise in the z-plane so that the petals are not completely flat and emulate the imperfection in nature. The pistil and stamen are relatively straightforward to generate, as they are just segments with ellipsoids at the end.

First render :

Texture Mapping

After petal generation has concluded, we plan to generate randomized veins on the petal (all originating from the center) with a jitter transform. We will look more into multijugate/whorled phyllotaxis and research how the macro structure of the petal can relate to the cellular texture of the petals to generate the petal texture.

Subsurface Scattering

Subsurface scattering (or SSS) is a mechanism of light transport in which light penetrates the surface of a translucent object, is scattered by interacting with the material, and exits the surface at a different point. The light will generally penetrate the surface and be reflected a number of times at irregular angles inside the material, before passing back out of the material at an angle other than the angle it would reflect at had it reflected directly off the surface. (Wikipedia)

Background

Rose petals are translucent and to achieve the realistic, silky, lifelike softness we must implement SSS. This may be achieved with the reflection model described in the paper by Hanrahan/Krueger. We will also study the structure and cellular layers of petals. So far, we have learned that two especially characteristic layers, such as upper epidermal cells which are dome-shaped and spongy cells which reflect much light, cause the unique appearance of rose petals.

Petal SSS

We will, amongst other things, need to modify the Monte Carlo integrator code. We are planning to implement SSS as described in the Hanrahan/Krueger paper, adapting the layers to the tissue structure of our blossoms. We will calcuate the radiance by summing the radiance from surface and subsurface scattering, and the transmitted radiance from the sum of the radiance from absorption and subsurface scattering. From these values we calculate the BRDF and the BTDF and take into account the Fresnel coefficients. Since the petals are very thin, we will experiment first with single layer SSS, but if the desired results cannot be achieved from this we will continue adapt our algorithms according to what we found out from studying the cellular structure of flower petals.

Links

last edited 2007-06-13 17:47:47 by PriscillaPham