‘Structure-from-Motion’ photogrammetry: A low-cost, effective tool for geoscience applications

Abstract

High-resolution topographic surveying is traditionally associated with high capital and logistical costs, so that data acquisition is often passed on to specialist third party organizations. The high costs of data collection are, for many applications in the earth sciences, exacerbated by the remoteness and inaccessibility of many field sites, rendering cheaper, more portable surveying platforms (i.e. terrestrial laser scanning or GPS) impractical. This paper outlines a revolutionary, low-cost, userfriendly photogrammetric technique for obtaining high-resolution datasets at a range of scales, termed 'Structure-from-Motion' (SfM). Traditional softcopy photogrammetric methods require the 3-D location and pose of the camera(s), or the 3-D location of ground control points to be known to facilitate scene triangulation and reconstruction. In contrast, the SfM method solves the camera pose and scene geometry simultaneously and automatically, using a highly redundant bundle adjustment based on matching features in multiple overlapping, offset images. A comprehensive introduction to the technique is presented, followed by an outline of the methods used to create high-resolution Digital Elevation Models (DEMs) from extensive photosets obtained using a consumer-grade digital camera. As an initial appraisal of the technique, an SfM-derived DEM is compared directly with a similar model obtained using Terrestrial Laser Scanning. This intercomparison reveals that decimetre-scale vertical accuracy can be achieved using SfM even for sites with complex topography and a range of land-covers. Example applications of SfM are presented for three contrasting landforms across a range of scales including; an exposed rocky coastal cliff; a breached moraine-dam complex; and a glaciallysculpted bedrock ridge. The SfM technique represents a major advancement in the field of photogrammetry for geoscience applications. Our results and experiences indicate SfM is an inexpensive, effective, and flexible approach to capturing complex topography.

Estimation of evapotranspiration of temperate grassland based on high-resolution thermal and visible range imagery from unmanned aerial systems

“…Orthomosaics were generated using Agisoft PhotoScan Professional (Agisoft LLC). The software reconstructs a three-dimensional point cloud from overlapping single images with a technique called Structure from Motion (Westoby et al 2012; Fonstad et al 2013; Smith, Carrivick, and Quincey 2016). In the first step, image alignment, information from the GPS unit of the UAS was used as a first estimate of camera location and orientation.…”

SF3M software: 3-D photo-reconstruction for non-expert users and its application to a gully network

“…3-D photo-reconstruction (3D-PR) based on structure-frommotion (SfM) algorithms has been applied to date to a large number of geoscience applications (James and Robson, 2012;Westoby et al, 2012;Fonstad et al, 2013). Although there has been a great advance in the last years regarding imagery collection (for instance, derived from the development of UAV (unmanned aircraft vehicle) platforms) and image processing (commercial as well as free software), the complete photo-reconstruction (PR) and analysis workflow frequently remains lengthy and not straightforward (Kaiser et al, 2014).…”

Overland Flow Analysis Using Time Series of Suas-Derived Elevation Models

“…Procedures for obtaining imagery using unmanned platforms and processing acquired data in photogrammetric software no longer require expert knowledge and experience. The high degree of automation in photogrammetric flight planning and execution and the availability of numerous software packages utilizing SfM algorithms make the extraction of threedimensional coordinates from sufficiently overlapping photography possible (Tonkin et al, 2014) even without camera location and orientation data (Snavely et al, 2008;Westoby et al, 2012). It has been demonstrated that this approach produces terrain models with resolution and data quality equivalent to or better than lidar (Carrivick et al, 2013;Fonstad et al, 2013).…”