3D graphics eBook - Course Materials Repository

Level of detail 74
Hierarchical LOD
Because hardware is geared towards large amounts of detail, rendering low polygon objects may score sub-optimal
performances. HLOD avoids the problem by grouping different objects together hlod . This allows for higher
efficiency as well as taking advantage of proximity considerations.
References
1. Communications of the ACM, October 1976 Volume 19 Number 10. Pages 547-554. Hierarchical Geometric
Models for Visible Surface Algorithms by James H. Clark, University of California at Santa Cruz. Digitalized scan
is freely available at http:/ / accad. osu. edu/ ~waynec/ history/ PDFs/ clark-vis-surface. pdf.
2. Catmull E., A Subdivision Algorithm for Computer Display of Curved Surfaces. Tech. Rep. UTEC-CSc-74-133,
University of Utah, Salt Lake City, Utah, Dec. 1974.
3. de Boer, W.H., Fast Terrain Rendering using Geometrical Mipmapping, in flipCode featured articles, October
2000. Available at http:/ / www. flipcode. com/ tutorials/ tut_geomipmaps. shtml.
4. Carl Erikson's paper at http:/ / www. cs. unc. edu/ Research/ ProjectSummaries/ hlods. pdf provides a quick, yet
effective overlook at HLOD mechanisms. A more involved description follows in his thesis, at https:/ / wwwx. cs.
unc. edu/ ~geom/ papers/ documents/ dissertations/ erikson00. pdf.
Mipmap
In 3D computer graphics texture filtering, MIP maps (also mipmaps) are pre-calculated, optimized collections of
images that accompany a main texture, intended to increase rendering speed and reduce aliasing artifacts. They are
widely used in 3D computer games, flight simulators and other 3D imaging systems. The technique is known as
mipmapping. The letters "MIP" in the name are an acronym of the Latin phrase multum in parvo, meaning "much in
a small space". Mipmaps need more space in memory. They also form the basis of wavelet compression.
Origin
Mipmapping was invented by Lance Williams in 1983 and is described in his paper Pyramidal parametrics. From
the abstract: "This paper advances a 'pyramidal parametric' prefiltering and sampling geometry which minimizes
aliasing effects and assures continuity within and between target images." The "pyramid" can be imagined as the set
of mipmaps stacked on top of each other.
How it works
Each bitmap image of the mipmap set is a version of the main texture,
but at a certain reduced level of detail. Although the main texture
would still be used when the view is sufficient to render it in full detail,
the renderer will switch to a suitable mipmap image (or in fact,
interpolate between the two nearest, if trilinear filtering is activated)
when the texture is viewed from a distance or at a small size.
Rendering speed increases since the number of texture pixels ("texels")
being processed can be much lower than with simple textures. Artifacts
are reduced since the mipmap images are effectively already
anti-aliased, taking some of the burden off the real-time renderer.
Scaling down and up is made more efficient with mipmaps as well.
An example of mipmap image storage: the
principal image on the left is accompanied by
filtered copies of reduced size.