UAV-Based Stereo Vision for Rapid Aerial Terrain Mapping

Abstract

Aerial terrain mapping has been used for many years to monitor natural habitats and ecosystems, assist in urban planning, and monitor trends in land usage. Recent improvements in digital imaging, LiDAR, and synthetic aperture radar have facilitated the generation of 3-D terrain models for analysis in these applications. Unfortunately,thesesystemstypicallyrequirelargemannedaircraftandsignificant post-processing of data before viewable results are produced. This inhibits use of these technologies in time-critical applications such as disaster relief, autonomous obstacle avoidance, and landing-zone assessment for a vertical take-off and landing aircraft. This paper describes a wide-baseline stereo vision system that enables near-real-time generation of dense 3-D terrain maps. The key advantage of computational stereo vision over monocular structure-from-motion is that terrain can be reconstructed from a single synchronized pair of calibrated images. The paper describes a working prototype, and presents a novel approach for combining separate stereo maps into larger terrain mosaics. The new stereo system and algorithm have an accuracy rangingfrom56cmto65cmacrossthefieldofviewatanaltitudeof40m.Also, dense correlation of the imagery generates over 2200 points/m 2 . The system weighs just 3.1 kg, roughly one-fourth the weight of comparable high-altitude mapping systems, at ca. one-tenth the cost. The paper also describes potential implementations usingField-ProgrammableGateArrays(FPGAs)andApplication-SpecificIntegrated Circuits (ASICs) for real-time operation.

Airborne radiation mapping: overview and application of current and future aerial systems

“…A 3D scanning system works in a similar way, but uses a beam dispersal attachment (often an oscillating block or rotating mirror) to divert the emitted beams in multiple directions to create a 'beam swathe' (Figure 5). Using this swathe combined with the physical movement of the system across a target area, a 3D point cloud can be produced, which can be processed into a 3D representation of the area (Glennie et al 2013;Stefanik et al 2013). The length of the laser pulses in both variations produces a minimum length for the observation beam; causing issues with overlapping reflections at distances smaller than the beam length.…”

“…This is the most common method of producing three dimensional reconstructions of an area with an accuracy of 10-90 cm both horizontally and vertically (Grenzdörffer, Engel, and Teichert 2008), although recent unpublished work within the University of Bristol has been able to obtain spatial resolutions of around 5 cm both horizontally and vertically from a flight altitude of 70 m. Stereovision (Sanada and Torii 2015) works using similar principles to photogrammetry, but uses two rigidly affixed cameras at different angles to the surface from each other to take photographs of the environment. The camera's shutters are synchronized by the carrying system to ensure that photographs are taken at the same time and that the motion of the carrying system does not affect the calibration (Stefanik et al 2013). A major problem with the use of photogrammetry is that the technique is not suited for imaging dynamic environments such as those with moving traffic or trees blowing in the wind as the method assumes a static environment (Stefanik et al 2013).…”

“…Lidar is defined as an 'optics remote sensing technology that measures properties of scattered and reflected light to find range and/or other information about a distant target' (Karp and Stotts 2012). Modern systems use the 'time of flight' method ( Figure 5) to measure the distance to the target surface (Glennie et al 2013;Karp and Stotts 2012;Stefanik et al 2013). There are two variations of the technology to consider for radiation mapping applications: (i) single point range finders and (ii) 3D scanning systems.…”

“…Photogrammetry and stereovision techniques may also be used to extract 3D information from a ground surface (Stefanik et al 2013). Photogrammetry uses a single moving camera to create a sequence of overlapping images.…”

“…Photogrammetry uses a single moving camera to create a sequence of overlapping images. Each of the images are then combined using correlated focal points and image matching algorithms to produce a three dimensional image of the area (Stefanik et al 2013). This is the most common method of producing three dimensional reconstructions of an area with an accuracy of 10-90 cm both horizontally and vertically (Grenzdörffer, Engel, and Teichert 2008), although recent unpublished work within the University of Bristol has been able to obtain spatial resolutions of around 5 cm both horizontally and vertically from a flight altitude of 70 m. Stereovision (Sanada and Torii 2015) works using similar principles to photogrammetry, but uses two rigidly affixed cameras at different angles to the surface from each other to take photographs of the environment.…”