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Imagery
Unlike an uncorrected aerial photograph, an orthophotograph can be used to measure true distances,
because it is an accurate representation of the earth's surface, having been adjusted for topographic relief, lens distortion, and camera tilt.
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LiDAR
For determining elevations, LiDAR ('Light Detection and Ranging' or 'Laser Imaging Detection and Ranging') is more accurate and cost-effective than other methods of photogrammetric compilation.
A laser beam from an aircraft platform scans the ground perpendicular to the line of flight, and the laser returns, or reflections, from the ground and foliage are processed to determine the ground elevations. As LiDAR penetrates tree cover, it provides the most accurate ground definition possible.
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