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Development of a digital terrain simulator for short-term forest resource planning Lemkow, Daniel Zwi

Abstract

This study describes the development of a desktop computer model (digital terrain simulator) for short-term forest planning. An overview of the applications currently developed for the terrain simulator is presented: (1) Collection of the required terrain elevations and forest inventory data; (2) Determination and production of map overlays of the topographic features: slope, aspect and elevation; (3) Design of logging settings for cable systems and placement of yarding roads; (4) location of forest-access roads; (5) Delineation of viewable areas and production of three dimensional representations of the terrain on a two dimensional surface; (6) Estimation of harvesting costs and wood volume production. The study then presents the theory required to implement each of the above components. Where possible, several different approaches are developed and compared. The elevation data base, describing the study area, is represented by a regular grid of elevations. The slope, aspect and elevation are computed for each of these grid units frost a geometric plane fitted to the ground surface using a least-squares procedure. An algorithm for producing map overlays of these attributes, in varying combinations, is given. The major emphasis in the discussion of the setting design module is on the prediction of loadpaths of cable yarding systems. The road design module concentrates on route projection. An algorithm is proposed that automatically locates a trial route between any two map locations. For producing three dimensional representations both orthographic and perspective projections are developed along with an algorithm to remove the 'hidden areas' in these three dimensional plots. The costing module presents methods for input of forest inventory data, using the same regular grid as for the terrain elevations. An algorithm deterministically simulates the yarding of the wood in each grid unit contained by the logging setting boundaries. Finally, the limitations of the model, due to computer technology and the quality and quantity of the data, are examined. Slow execution speed, in several instances, dictated the use of the least accurate approach; this occurred in the input, yarding design and costing modules. This also made it necessary to use orthographic instead of the true perspective projection for producing three dimensional representations. The determination of earthwork volumes, for road construction, was deemed inappropriate, due to the generally poor precision of available maps. Soils information, although important for estimating costs of yarding and road construction, was not included because of its limited availability. The map overlays of slope, aspect and elevation could be easily extended to include soils and land-use data, thereby offering a more complete and useful retrieval system. Although full implementation of the terrain simulator has not been possible, this study demonstrates the feasibility of implementing a comprehensive short-term forest planning model, designed for a desktop computer.

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