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ŠUMARSKI LIST 1-2/2015 str. 40     <-- 40 -->        PDF

FR1, FR2 and FR3 which propose new forest road options. The new forest roads were mapped in GIS considering the longitudinal gradient of the road, the terrain steepness, and the positive and negative cardinal points identified in the field survey, based on contour lines derived from a DEM with accuracy of 20 m.
Raster method – Rasterska metoda
This method assumes that all harvested timber is located on the skid trails. The skid trails were first converted from vector to raster format. The skid trail raster (with 12.5 m sized cells) was updated with altitudinal information obtained from the DEM. Using Spatial Analyst Tools™ in ESRI® ArcGIS, the least accumulative path distance for each cell of the skid trail raster to the nearest forest road were calculated (Figure 1), considering horizontal and vertical constraints (Equations 10 and 11). Each cell of the skid trail raster contains the slope distance to the nearest forest road, adjusted with the elongation occurred due to the sinuosity of the trail. The path distance from cell a to the adjacent cell b and the accumulative path distance from cell a to cell c were computed as follows (ESRI ArcGIS Resources 2013):
In case the movement from one cell to the adjacent cell was diagonal, Equation (10) was multiplied with . In Equation (11), a1 represents the path distance between the adjacent cells a and b, calculated with Equation (10). The real mean extraction distance (SDe) of the study area is given by the arithmetical mean of the values contained by each cell of the skid trail raster. Similarly, the minimum and maximum real extraction distances for all infrastructure scena­rios were determined.
The automation of work flow processes was performed in Model Builder™, an extension of ESRI® ArcGIS which allows workflows to be combined in interactively linked sequences using DEMs, GIS datasets and results of previous calculations making calculations faster and easier (Allen 2011). Automation models were developed for all methods presented below.
Centres of gravity (CGR) method – Težišna metoda (CGR)
This method assumes that harvested timber is concentrated in the centres of gravity of each forest management unit (Ciubotaru 1996; Pentek et al. 2005). The extraction