Author(s):
D.A. Maxwell, R. Turpin
Publication Date
August 1968
Abstract
Although the systems approach to design is usually thought of as having applications. only in the field of hardware systems design, from whence it came systems methodology and philosophy are also applicable to the design of computer software systems. The NGI (Numeric Ground Image) Systems Design study is an example of the systems approach to the design of a computer software system.|The NGI System furnishes the highway engineer with a method for approximating the terrain surface with a numerical surface. Traditional highway design practice has required the use of cross-sections to represent the terrain. The use of the numerical surface approach, instead of the cross-section method, eliminates some terrain representation problems associated with the traditional cross-section method. For example, if the horizontal alignment of a roadway is shifted, a new and separate set of cross-sections corresponding to the new alignment must be obtained. This new set of cross-sections is necessary because the old set was directly referenced to the old alignment. This is not true of the numerical surface approach because it is not directly referenced to any specific alignment.|The NGI System is designed to interface with FORTRAN "driver" programs. In general, whenever the interfacing program requires an elevation at a specific horizontal position, it passes the X and Y coordinates of that position to the NGI System through the appropriate interface. The NGI System computes the Z (elevation) corresponding to the X and Y and passes it back to the original program through the same interface. The nature of the interfacing program can vary from, say, earthwork analysis to contour plotting.|The NGI System computes the required elevations in this manner. The ensemble of terrain data points (all measured with respect to the same coordinate system) is divided into rectangular sectors and then stored by sector in a direct access device. As the sector data points are required for elevation computations, they are brought from storage into the core. The cluster of data points surrounding the required point is then selected from the sector data. The elevation of the desired point is obtained from a surface which has been fit by least squares to the cluster of terrain data points.|At this stage of development the NGI System is not a general purpose engineering tool to be used by the unwary. However, once the operating characteristics of the NGI System are determined and surface technology is extended into engineering design, it holds the promise of becoming a highly effective highway design technique.
Report Number:
120-1
Link(s):
Document/Product
http://tti.tamu.edu/documents/120-1.pdf
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