Geol 702H - 3-D Modeling Principles
Roland Schweitzer
modified by J. Louie, Feb. 27, 1996
3-D Modeling and Animation Steps
Geometry Creation
Material Design
Rendering
Animation (create the action)
Sources of Geometry:
CAD
``Real world'' sampling
``Free hand'' design
from primatives
Bezier & NURBS curves
fractal surfaces
Boolean operations
CAD
CAD programs can save information in standard file formats such as
DFX or IGES.
Many animation systems will preserve the hierarchical structure of
the orginal design.
Motion and material animation can then be applied just as the
geometry was created in the animation system.
``Real World'' Sampling
The three dimensional analog of scanning an image.
The scanning returns coordinates in three dimensions of primatives
that describe the object being scanned.
Motion and material animation can then be applied just as the
geometry was created in the animation system.
Geometric Primatives
Example of ``wireframes'' showing edges of intersecting triangles that
approximate a simple plane, spheres, tetrahedron, and cube.
The
Cyberview-X interface at the
Univ. of Minnesota's
Geometry Center provides a way to view your choice of hundreds of
different objects interactively from any viewpoint, using your forms-capable
WWW browser. Their computer calculates the viewed image and sends it back
to you. Presently it supports only wireframes and simple shading.
Fractal Geometries
Example of a synthetic landscape created by assigning the elevation of
triangle vertices a random difference from the elevations of their neighbors.
The elevation variations obey a fractal geometric exponential relation.
The colors scale to the elevations, again with fractal variations.
Created on a Macintosh with the
Fractal! 1.2
software package.
Example of a synthetic object created as a collection of geometric primative
objects whose orientation and connectedness obeys a fractal relationship.
Created at the Univ. of
Minnesota's Geometry Center.
Animation systems allow the user to specify the exact material
characteristics of each object.
For example:
- metalic or non-metalic highlights
- color
- diffuse intensity
- ambient intensity
- highlight shininess
- highlight brightness
- opacity
- reflectivity
- index of refraction
- gloss
- translucency
- texturing or ``bump mapping''
- image drape over surface
Rendered image with color and diffuse reflectance intensities applied to
the wireframe geometries above.
Image rendered after making some surfaces transluscent and reflective.
The viewpoint was also moved.
Raytracing techniques:
Light is computationally cast on the scene.
Reflections and refractions are calculated, and the material aspects
of the objects encountered are used to determine the color and value of the
pixel.
Software rendering allows for effects found only in the most
expensive hardware (transparent surfaces, for example) to be rendered
on inexpensive hardware.
Image rendered after applying walnut and granite ``texture maps'' to some
surfaces, and a ``bump map'' to other surfaces (some transluscent).
The geometric examples were rendered on a Sun with SunVision software.
When logged into a Seismology Sun, click to download the file
texture.scene, which is a script
that places objects and controls how to render them.
Give the Sun command ``sunvision'', then click on the
``Sun GV'' button to start the geometry viewer and editor, and also the
``Sun ART'' button to start the rendering engine. In Sun GV open
the ``texture.scene'' scene file to see the objects and their
attributes, and then export the scene. In ``Sun ART'' import the scene and
press the ``Render'' button.
For a Macintosh, you can
click here
to download the ``Vort'' software package, which provides similar functionality.
For lists of 3-d geologic mapping, modeling, and visualization software,
click here.
The video sequence here
from a course at the Cornell Theory
Center
shows many rendered frames of spherical objects with texture maps
applied. Between each frame the objects rotate and the viewpoint and
direction of view change. To specify the six coordinates needed for each
view (three for the viewpoint, three for the direction) the students only
defined them for certain ``keyframes'' where the view location or direction
changes course. Between the keyframes, the rendering program automatically
interpolates the intermediate views.
This MPEG clip (original
here)
from the
JPL Imaging Radar Program texture maps a radar image onto a topographic
surface, then renders animation frames by describing a ``flight path'' in the
3-d model space.
This QuickTime clip from the
Disney movie ``Toy Story'' shows
the combination of advanced texture mapping, articulation and hierarchy
of objects, and detailed keyframe animation required for realistic scenes.