The online GIS SIGPAC of the Spanish Ministry of Agriculture, Fisheries and Food was used as a convenient tool for the required measurements and for providing an airphoto basemap in the field. The length and width of the minimum area of interest are 128 m by 120 m (Fig. 9-15, red box). As this oblong is proportionally wider in comparison to the image sensor, the target scale needs to be calculated by inserting the width values into Equation 3-1:
with dw being the image width and Dw, ground area width. This scale results in a longer area covered than necessary (area length Dl = 22.2 mm x 8108 = 180 m, see green outline in Fig. 9-15). To double check, consider the image scale resulting from the length values (1/5766). This larger scale would result in too small a ground coverage width (14.8 mm x 5766 = 85.34 m) and is, therefore, insufficient for covering the whole area of interest.
From Equation 3-2, the target flying height can be determined as:
Hg = f x s = 20 mm x 8108 = 162.16 m and the ground size of a pixel as:
Thus, the whole area of interest would fit into a single image if the camera was positioned and oriented as depicted in Figure 9-15 at a flying height of 162 m, yielding a resolution of 5.2 cm on the ground.
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