Abstract
The use of action cameras for photogrammetry purposes is not widespread due to the fact that until recently the images provided by the sensors, using either still or video capture mode, were not big enough to perform and provide the appropriate analysis with the necessary photogrammetric accuracy. However, several manufacturers have recently produced and released new lightweight devices which are: (a) easy to handle, (b) capable of performing under extreme conditions and more importantly (c) able to provide both still images and video sequences of high resolution. In order to be able to use the sensor of action cameras we must apply a careful and reliable self-calibration prior to the use of any photogrammetric procedure, a relatively difficult scenario because of the short focal length of the camera and its wide angle lens that is used to obtain the maximum possible resolution of images. Special software, using functions of the OpenCV library, has been created to perform both the calibration and the production of undistorted scenes for each one of the still and video image capturing mode of a novel action camera, the GoPro Hero 3 camera that can provide still images up to 12 Mp and video up 8 Mp resolution.
Highlights
During the last few years, passive sensors providing visual image information [1], as well as the development of software solutions for the extraction of point clouds from a set of un-oriented images have received increasing attention, from the surveying community, and from non-experts
The reason is due to some clear advantages provided from these systems: the improved resolution and sensitivity of photo sensors and the availability of low cost off-the-shelf digital cameras which can be used in several photogrammetric applications, such as aerial mapping or emergency documentation
A full review of camera calibration methods and models developed in the last few years can be found in [3,4,5] describing the commonly adopted methods such as Tsai [6] or Zhang [7]
Summary
During the last few years, passive sensors providing visual image information [1], as well as the development of software solutions for the extraction of point clouds from a set of un-oriented images have received increasing attention, from the surveying community, and from non-experts (such as archeologists). Nowadays there are several software applications (i.e., Photomodeler, Agisoft Lens, iWitness, MicMac, 3DF Zephir, etc.), mainly produced by the computer vision scientific community, that can automatically perform camera self-calibration They offer the possibility to work with several cameras and sensors to obtain dense point clouds or 3D models suitable for different fields of applicFation. In the wide panorama of low-priced consumer grade devices [8] (including nowadays even smartphones or other similar mobile devices) [9,10], action cameras are more widespread and have been used more and more during extreme activities such as free fall, parapent flying, underwater swimming and diving Their photogrammetric use though has not been easy since they could not supply high resolution still images and video and their geometry are far away from the theoretical model of central projection due to their wide angle or fish eye lenses. The camera is very light and it can be controlled through a WiFi connection from a cell phone or tablet [17]
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