Three-dimensional Model Of Object Research Articles

Recent developments in molecular graphics: visualization of chemical structures and properties

As three-dimensional models of chemical objects are essential tools for understanding their intimate structure and function, nowadays molecular graphics techniques allow building, visualizing, and manipulating, of complex molecular structures and their related properties. This paper presents several developments recently achieved in this field, namely: the representation of macromolecular structures such as proteins; the modelization of molecular envelopes as dot surfaces, mesh surfaces, and solid models; the evaluation and visualization of color-coded reactivity indices based on intermolecular interaction energies. The last application is shown to be particularly useful in several applications, such as molecular recognition and drug design.

Feature extraction from boundary models of three-dimensional objects

An algorithm for extracting certain classes of form features from a relational boundary model of an object, called the generalized edge-face graph (GEFG), is described. The GEFG provides a face-based topological description of the object boundary and encodes the minimum number of relations needed in the recognition process. The feature identification and classification are based on the analysis of the connectivity properties of the edge-face graph associated with the GEFG and on some geometric considerations. The result is a hierarchical graph decomposition of the object boundary into components representing form features.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Solid modeling in robotic vision

Robotic vision has been usually considered a computational task which processes images in order to obtain three-dimensional models of objects and therefore is image driven. However, this is not the only possible approach. A different approach is presented which is driven by solid modeling, where a common three-dimensional representation coordinates the activities of early processing modules.

Object representation by means of nonminimal division quadtrees and octrees

Quadtree representation of two-dimensional objects is performed with a tree that describes the recursive subdivision of the more complex parts of a picture until the desired resolution is reached. At the end, all the leaves of the tree are square cells that lie completely inside or outside the object. There are two great disadvantages in the use of quadtrees as a representation scheme for objects in geometric modeling system: The amount of memory required for polygonal objects is too great, and it is difficult to recompute the boundary representation of the object after some Boolean operations have been performed. In the present paper a new class of quadtrees, in which nodes may contain zero or one edge, is introduced. By using these quadtrees, storage requirements are reduced and it is possible to obtain the exact backward conversion to boundary representation. Algorithms for the generation of the quadtree, Boolean operations, and recomputation of the boundary representation are presented, and their complexities in time and space are discussed. Three-dimensional algorithms working on octrees are also presented. Their use in the geometric modeling of three-dimensional polyhedral objects is discussed.

Matching three-dimensional objects using a relational paradigm

A relational model for describing three-dimensional objects has been designed and implemented. The model, which provides a rough description to be used at the top level of a hierarchy for describing objects, was designed for initial matching attempts on an unknown object. Each description is in terms of the set of simple parts of an object. Simple parts can be sticks (long, thin parts), plates (flat, wide parts) and blobs (parts that have three significant dimensions). The relations include an attribute-value table for global properties of the object, the properties of the simple parts, binary connection and support relationships, ternary connection relationships, parallel relationships, perpendicular relationships and binary constraints. An important use of the model is to characterize the similarity and differences between three-dimensional objects. Toward this end, we have defined a measure of relational similarity between three-dimensional object models and a measure of feature similarity, based only on Euclidean distance between attribute-value tables. In a series of computer tests, we compare the results of using the two different similarity measures and conclude that the relational similarity is much more powerful than the feature similarity and should be used when grouping the objects in the database for fast access.

Alternative representations for geometric models of three-dimensional free-form objects

Alternative representations for geometric models of three-dimensional free-form objects