*Note: This eBook describes the invention disclosed as US Patent: (Patent Pending – March 2018) Method and System for Developing Non-traditional (non-linear and non-parallel) Gently Curving Camera Trajectories for Collecting Digital Aerial/Terrestrial Photography for Construction of 3D Topographic Models Using Structure-from-Motion (SfM) Techniques.
Abstract: A method and system is described for prescribing and constructing nontraditional camera placement trajectories (a series of specific waypoints) to more effectively capture digital image networks for the production of geometrically and geographically correct 3D point cloud models using Structure-from-Motion (SfM) techniques – the “work”. The constructed waypoints define gently curving trajectories which a) guide photographers in the placement of cameras and/or b) provide pathways for ground vehicles and/or flight lines for manned/unmanned aircraft carrying an adequate payload of vertical and/or oblique cameras of various types sufficient for the prescribed work. The unique, gently curving, convergent, non-linear, non-parallel, continuously changing shape of the camera trajectories produced using this disclosed method and system are necessary and sufficient to significantly contribute to the resolution of identified systematic errors previously experienced in SfM production of 3D topographic models (point clouds) using digital photographs captured using traditional straight, linear, parallel camera trajectories.
Once constructed, the unit-scale trajectories (templates) are re-scaled, translated, and rotated into a real-world Cartesian coordinate system to provide optimal camera deployment trajectories necessary and sufficient to support the collection of digital images (photographs) of point, line, area, and/or longer narrow corridor targets.
The disclosed method and system of constructing trajectories for aerial/terrestrial collection of vertical and/or oblique digital photographs a) provides a unique diversity of view aspects for all types of targets, b) affords a known constant camera mounting angle tangent to the trajectory – thus avoiding the need for using gimbal-mounted cameras and their associated control issues, as well as c) tempers the SfM workflow’s propensity for producing the “dome” effect. Restated, most importantly the disclosure tempers the propensity for introducing systematic error when the SfM workflow is subjected to digital imagery captured using traditional (linear, parallel) camera trajectories.
Refer to the fourth bulleted item above: The resulting few favored trajectories would be selected by a camera operator (photographer) based on a) the physical and operational characteristics of the chosen camera [sensor array size/focal length/shutter speed/image size at the chosen range-to-target], b) the axial/lateral (forward/side-to- side) image overlap requirements of the SfM software available for processing the photographs to be collected, and c) if the camera is to be moving along a selected trajectory, the forward speed of movement and camera mounting angle(s). For the moving camera, the selected few trajectories provide an inherent operational efficiency with the one occupied trajectory practically aligning with the next (to-be-occupied) trajectory – providing a continuous path and thus saving transition time and energy – refer ahead to Figure 16. Although the effective capture of quality digital images serves as the impetus for this invention, the camera operator’s selection of a) the camera itself and b) the camera’s deployment mechanisms are outside the scope of the current disclosure.
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