It is typically done using LiDAR or ground measurements. Traditionally measuring Digital Surface Model has been extremely difficult and expensive. True Orthophoto gives a vertical view of the earth’s surface, eliminating building tilting and allowing a view of nearly any point on the ground. True Orthophoto, on the other hand, is processed using Digital Surface Model that maps every shape and object visible on the ground (including vegetation and man-made objects). In orthophotos, you will often see an effect where the terrain representation is very accurate, but you will see a tilt in the buildings and other tall structures which is an effect of using DTM that only maps the natural shape of the earth (excluding vegetation and all man-made objects and structures). source: nFrames SURE Softwareįirstly, Orthophoto is an effect of photogrammetry processing that uses the Digital Terrain Model (DTM), typically seen in the traditional airborne photogrammetry. Don’t worry, I will explain it all to you! Orthophoto (left) vs. Some of the terms apply mainly to the traditional photogrammetry and some apply more to the low altitude photogrammetry. Below I will try to define some key terms that you may see out there. Also, I have noticed that some of these terms have a slightly different meaning in different languages.
What I’ve noticed though, is that when you commoditize a field of engineering, the previous scientific terms start to live their own lives. The drones and so-called “low-altitude photogrammetry” is ubiquitous. This helps them greatly in farming, construction, urban planning, energy, mining, and many other sectors. They fly drones, capture the data, and process it seamlessly to get orthomosaics and Digital Surface Models (DSM). Photogrammetry is now practised every day by hundreds and thousands of people around the world. Today, the science of photogrammetry is in a totally different place due to the rise of drones over the past 7-8 years. The data was used mainly by governments and the military, and it was extremely expensive. Back then, it was a field understood and practised by a fairly small and closed group of engineers. Initially being fully analogue, it is gradually being digitalized for the past 30-40 years. The science of photogrammetry has been developing for more than a century.
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