An ortho-aerial photograph is helpful and effective in obtaining the status and estimation of (LU/LC) area in flat regions. However, A. formosana grows well in steep regions where trees cannot grow, and the terrain is extremely steep in this reserve. Therefore, the area of A. formosana growth might be underestimated if we use conventional methods to estimate growth area and if we consider the terrain in this study.
The slope degree was calculated with DTM by using Horn’s algorithm (Horn 1981), which is the best estimation method (Skidmore 1989) in ArcGIS. The hypotenuses of all the pixels were calculated using the normal RS data and slope degrees. Figure 18.3 is an exaggerated example to explain the concept of the trigonometric function. The raster data of the hypotenuses were calculated pixel by pixel by using Eq. 18.2:
b = a x sec в (18-2)
where a = adjacent, b = hypotenuse, and в = slope degree (slope degree ^ 180 x n).
Fig. 18.4 Flowchart for the analysis procedure for A. formosana distribution, area, and niche