Best Practices When Using Multi-Rotor Consumer UAVs for Photogrammetric Mapping: Limitations and Possible Solutions
Photogrammetry has seen great technological advancements since its inception almost 150 years ago. Today digital cameras are being mounted to unmanned aerial vehicles (UAVs) and used for aerial surveying and photogrammetry. Within the past decade, consumer-grade multi-rotor UAVs have become viable platforms for performing low altitude aerial photogrammetry. Modern-day photogrammetric software has become so advanced that processing requires minimal intervention for the user to produce results. Although performing low altitude aerial photogrammetry can achieve a high ground sample distance, at these low altitudes, artifacts and inadequacies begin to appear within produced digital surface models and orthophotos. Additionally, many flight plan and post-processing software packages limit or even hide features that prevent users from fully taking advantage of photogrammetric practices and the capabilities of consumer multi-rotor UAVs. In this study, through the modification of flight plan CSV files, several different methods are explored to re-introduce photogrammetric practices to the multi-rotor UAV platform in an attempt to improve the production of digital surface models and orthophotos. Flight plans are modified to allow for images to be captured in portrait orientation using a fixed camera to achieve an improved project depth accuracy. By further modifying flight plan CSV files, automated aerial camera calibration flight plans are created while incorporating traditional terrestrial calibration techniques. The use of an automated camera pre-calibration flight plan is found to outperform auto-calibration workflows. Lastly, with the ability to modify a flight plans CSV file, the Maltese-cross camera network is simulated using a single camera onboard a consumer-grade multi-rotor UAV to achieve simultaneous horizontal and vertical mapping at low altitude. These approaches combine to allow for improved data acquisition and post-processing when using consumer-grade multi-rotor UAVs to produce high-quality digital surface models and orthophotos. Improving these photogrammetric products allows for users to take full advantage of the features of consumer multi-rotor UAVs while ensuring photogrammetric best practices are maintained. The ability to modify a flight plan introduces the possibility of creating more complex automated flight plans for improved workflows.