McGlone - 1 
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SOME CONSIDERATIONS IN 3D 
OBJECT MODELING 
Chris McGlone 
Digital Mapping Laboratory 
School of Computer Science 
Carnegie Mellon University 
5000 Forbes Avenue 
Pittsburgh, PA, 15213-3891 
jcm@cs.cmu.edu 
1. Introduction 
Our goal is to use images to describe the world; object models are how we ’’talk 
about” objects in the world. The language we define by our models determines 
what we can say about objects, how easily we can say it, and how well we can be 
understood by others. 
There are a large number of competing model types—languages—currently in use. 
Rather than a detailed technical discussion of model types, this paper will focus 
on model selection criteria. The selection of a model type must be based on more 
than purely computational or algorithmic considerations. While it is important for 
the chosen model to be usable efficiently by the vision algorithms, for robust and 
meaningful results other considerations must be taken into account. 
This paper briefly discusses selection criteria in the context of model types, pointing 
out comparative strengths, weaknesses, and tradeoffs. The optimal model type can 
change at each phase of the computer vision process, from the initial processing to 
delivery of models to an end user; pros and cons of models for each phase will be 
discussed. The design decisions made in some existing systems will be discussed. 
Finally, some conclusions will be outlined. 
2. Model types 
A few main types of models and their variations have become standard within com 
puter vision research. Some have been borrowed from computer aided design, such 
as constructive solid geometry (CSG) models, while others have been developed by 
the vision community. This section gives an overview of some general types of object 
models, in preparation for discussion of their specific applicabilities and properties 
later in the paper.