A system for the construction of a three-dimensional block diagram representation from two-dimensional data

The purpose of this study was to develop an interactive computer program to draw three-dimensional block diagrams of discontinuous surfaces from two-dimensional data using parallel lines to represent the surfaces. Unlike all parallel-line or fishnet programs, this program is unique in that the surface area at the top of these polygons was the same as the base surface area of each respective polygon. This is different from the existing discontinuous surface plotting programs, where the top is smaller due to incremental plotting techniques of sloping lines. The construction of these polygon-base columns was accomplished by having two Z-values for each XY point. Hidden lines were removed by keeping track of the starting and ending points of all new visible vectors and comparing them with the visible portions of all vectors which had been plotted. By starting in the lower front corner, plotting from left to right, and keeping track of the top line, the program needed only to know when the current vector being plotted changed states, that is, whether it was visible or invisible.

DISCON, the FORTRAN IV program created for this study, was used to plot a coordinate set of the ninety-five counties for the State of Tennessee as an example. . The height of the polygons, corresponding to the third dimension of the polygons or, in this case the counties, were 1970 population data. However, any two-dimensional surfaces (with any third dimensional values assigned) could be used. With the data set defined, evenly spaced parallel lines can be overlaid at either 0°, 45°,

90°, or 135°. DISCON finds the intersections between each parallel line and each line segment of each polygon. The intersection of these diagonals and polygon line segments are saved in a file for further data manipulation. These data manipulations consisted of rotation of the data base file of intersection in a Y and Z rotation. . DISCON next executes the hidden-line elimination portion of the algorithm, computes the viewing angle, and displays the results on the TEKTRONIX terminal and/or plotter. At this point, the user has the option to return to the original base file, enter new data, change the input parameter for the rotation in a X,Y,Z direction, and view the surface in a different representation.

The results presented in this thesis show that DISCON is a practical program to construct a three-dimensional block diagram of discontinuous surfaces from two-dimensional data using parallel lines to represent the surfaces.