Effect of camera calibration on the accurate generation of digital elevation models from UAV acquired low percentage overlapping images.

Abstract

Using low percentage overlapping images (15-20% sidelap and endlap) acquired from a DJI Phantom 3 Quadcopter UAV, and a 4K resolution digital camera (FC300X), an attempt has been made in this research to investigate the impact of camera calibration on the accuracy of Digital Elevation Models (DEMs) using four (4) possible case scenarios which are: (1) Processing without calibration, (2) Processing with calibration before optimization of camera alignment, (3) Processing with calibration during optimization of camera alignment and (4) Processing with calibration after optimization of camera alignment. The images were processed using Agisoft photoscan digital photogrammetric software. Eastings, Northings and Height coordinates of ground control points were extracted from the DEM generated based on these four conditions and compared with the coordinates of the same points established using Hi-Target Differential Global Positioning System (DGPS) receivers. Using the National Standard for Spatial Data Accuracy (NSSDA), the result obtained showed that though the impact was quite trivial on the Eastings and Northings coordinates extracted from the DEMs produced under these four camera calibration conditions (each producing a horizontal accuracy of 0.003786) and more evident on the height values, DEM generated by calibrating the camera before optimization of camera alignment yielded the best accuracy (with vertical accuracy of 0.08956) when compared to the other three conditions. It is thus recommended that the operation of camera calibration be performed before the optimization of camera alignment when processing UAV acquired image data for DEM production using Agisoft photoscan digital photogrammetric software.