The present invention is a GIS system in which topological information is classified as geometrical objects and uses a region identifier and a geometry attribute to reconstruct each topological feature. The present invention starts from the geometrical objects representing topological features. Each geometrical object has an entry including a region identifier attribute and a geometry attribute defining the geometry of a complete representation of the feature. These geometrical objects are complete in that an entry of the object attribute includes a record for a geometry attribute defining the complete geometry of a complete representation of a topological feature. These complete geometrical objects need not inherit attributes from other objects. The objects are classified as either a polygon object, polyline object, point object or raster object and stored in a respective object-based database. Using this data structure, a topological region can be displayed in real time by accessing this object-based data structure and loading the data structure associated with the topological region into a buffer. The geometrical objects associated with the topological region are then fetched from the buffer and loaded into a virtual blackboard. The fetched geometrical objects are then drawn on a display in real time.

Object-based geographic information system (GIS)

Disclosed is a method for displaying a topology having topological features on a display. The method includes dividing the topological region into tessellations. An object-based database is accessed which comprises geometrical objects representing the topological features with each geometrical object associated with a particular tessellation. The geometrical objects are one of a polygon object, a polyline object and a point object representing the topological features. A tessellation is selected to be displayed. The geometrical objects are fetched which are associated with the tessellations to be displayed. The fetched geometrical objects are drawn on the display.

Tiling of object-based geographic information system (GIS)

While executing the standard graphics processing steps, problem polygons (ie, those outside of a defined clip volume) are buffered for later processing, while the standard graphics processing continues, without the need for periodically reformatting data and performing clipping After either a predefined number of polygons have been stored at the buffer location, or at such time as a change in the rendering state occurs, the buffered polygons are clipped

Method and apparatus for deferred clipping of polygons

A method and system are disclosed for providing a more accurate position of a mobile receiver even though a signal received by the mobile receiver indicating the position of the mobile receiver is inaccurate. The received signal is used as an estimated indication of the position of the mobile receiver. A database comprises geometrical objects representing navigable routes. The geometrical objects include a geometry attribute defining the geometry of a complete representation of the navigable route. A geometrical object representing a navigable route is determined where the mobile receiver is probably located. The estimated position of the mobile receiver can then be compared against the geometry of the navigable route and against the previous positions in which the mobile receiver was located. The estimated position of the mobile receiver can be adjusted if necessary to provide a more probable position of the mobile receiver.

Predictive drop and load algorithm for an object-based geographical information system

A vehicle navigation/position system (10) investigates road segments having start and end coordinates stored in a road map data memory (13). The system determines what road segments have at least a portion inside a rectangle of interest (ROI-100) about an estimated vehicle position (101). Map matching then corrects vehicle position by locating vehicle position on one of the road segments inside the rectangle of interest. Vehicle location/navigation information is then provided. A computer (11) identifies road segments as inside the rectangle of interest (100) by creating electrical signals associated with each road segment start/end coordinate as compared to boundary coordinates of the rectangle. These electrical signals identify the road segment coordinates with respect to areas (B-I) surrounding the rectangle of interest (A). For road segments extending between opposite middle side areas (B-I, C-G), the computer (11) determines the road segment inside the rectangle of interest, and the road segment is added to a list.

Vehicle map position determining apparatus

This paper describes a new alorithm for clipping a line in two dimensions against a rectangular window. This algorithm avoids computation of intersection points which are not endpoints of the output line segment. The performance of this algorithm is shown to be consistently better than existing algorithms, including the Cohen-Sutherland and Liang-Barsky algorithms. This performance comparison is machine-independent, based on an analysis of the number of arithmetic operations and comparisons required by the different algorithms. We first present the algorithm using procedures which perform geometric transformations to exploit symmetry properties and then show how program transformation techniques may be used to eliminate the extra statements involved in performing geometric transformations.

https://www.cs.drexel.edu/~david/Classes/Papers/p253-nicholl.pdf

An efficient new algorithm for 2-D line clipping: Its development and analysis

A method of clipping polygons in two dimensions, in which if a vertex is outside a boundary line, the succeeding vertex is handled as it is also outside the same boundary line until determined to be otherwise, in which if a vertex is in the window, the succeeding vertex is handled as it is also in the window until determined to be otherwise. This method also produces the fewest vertices after clipping a polygon. A method for clipping polylines is also derived from this method.

Polygon and polyline clipping for computer graphic displays

Of the two major approaches to line drawing, run-length slice algorithms are seldom used because of the division operation deemed necessary in these algorithms. The biggest advantage of these algorithms, the reduction of additions used, is considered outweighed by the division used. In this paper, a new run-length slice algorithm that does not require a division operation is presented. Furthermore, it uses the double-stepping paradigm in incremental line drawing algorithms to reduce the number of additions used by at least half.

For sufficiently long lines, this algorithm uses at least 50% fewer arithmetic operations than Wu et al.'s bi-directional double-step incremental algorithm. But because of its high initialization cost, for short lines, it is less efficient. For a line with endpoints (0,0) and (δx, δy), the strategy is then to use the bi-directional Bresenham algorithm for very short lines (δx 110).

A Run-Length Slice Line Drawing Algorithm without Division Operations

Problems in geometry often possess symmetry properties that may be exploited in order to develop solutions. Algorithms based on these symmetry properties will frequently use geometric transformations to transform one case into another (symmetric) case. One advantage of this approach is that the algorithm avoids enumeration of cases and thus is shorter and generally easier to read. One disadvantage is that some additional execution time is required to perform these transformations. We describe how simple program equivalences may be used as program transformations to eliminate this additional execution time from programs that use geometric transformations. This approach has been used to develop an efficient implementation of a new algorithm for the two-dimensional line-clipping problem.

Performing geometric transformations by program transformation

Functional programming languages have been advocated as a means for writing more reliable programs, although imperative programming languages permit more efficient execution on conventional computer hardware. The authors advocate a means of using a functional notation to annotate imperative programs and present a method for verifying that the annotated sections of code achieve the results specified in the annotation. Examples are given to show how the method is used. These demonstrate that this approach to program correctness leads to verification conditions which are briefer, but more numerous, than those which result from verifying more conventionally annotated programs. A goal of the article is to provide a technique to facilitate the activity of operational decomposition in a formal method in which refinements of specifications to implementations are made.

Tina M. Nicholl

Papers

An efficient new algorithm for 2-D line clipping: Its development and analysis

Polygon and polyline clipping for computer graphic displays

A Run-Length Slice Line Drawing Algorithm without Division Operations

Performing geometric transformations by program transformation

The use of functional annotations in verifying imperative programs