Page A3 Appendix A - Identifying the Kurt Franz Camera Shadow Height Measurements The height of several features imaged on the ground shots was determined as follows. First, the sun elevation () and azimuth () was established at the time the aerial photography was exposed. The azimuth was measured directly on the aerial frame after it was accurately aligned with true north. Shadows cast by buildings and trees were then measured, and an average taken. It was found that on the frames of the GX120 mission, = 90 degrees. That angle, in conjunction with the geographic coordinates of the camp and the time of year, was then used to compute the local sun time (t) and elevation angle. The results were: t =0634 AM, and = 24 50m. The last step was to measure on the aerial photos the length of the shadows cast and then to compute the heights of the features casting them. This is given by elementary trigonometry by: Height = SL * Tangent() . Where: SL = shadow length, measured on the aerial photos. Other Height/Ranging Measurements The distance of objects from the ground camera whose height could be estimated with some confidence was also computed as a further check. Estimates relied on internal clues contained in the images. Figure A3, shows a well and two of the Jewish workers. It has been enlarged from a Kurt Franz picture. A fairly good assumption is that the height of the figure on the left is about 1.7 or 1.8 meters. Given this assumption, the scaled height of the structure used to support the windlass shaft is 1 meter. The well shown here is also visible in the previous photograph ( Figure A1 ) as element number 6. To determine the distance from the camera station, one must knows the height of the feature in object space; the respective measurement in the image space; and the focal length of the camera. The distance to the object (D(o) is then given to a first approximation by the following equation (see Figure A4:) D(o) = {FL * H(o)}/H(i) , FL = Nominal focal length of the camera H(o) = Estimated height of the object Where: H(i) = Measured image height of the object SF = Scale factor to compensate for enlargements Previous Next
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