Abstract
Production of digital terrain model (DTM) is one of the most usual tasks when processing photogrammetric point cloud generated from Unmanned Aerial System (UAS) imagery. The quality of the DTM produced in this way depends on different factors: the quality of imagery, image orientation and camera calibration, point cloud filtering, interpolation methods etc. However, the assessment of the real quality of DTM is very important for its further use and applications. In this paper we first describe the main steps of UAS imagery acquisition and processing based on practical test field survey and data. The main focus of this paper is to present the approach to DTM quality assessment and to give a practical example on the test field data. For data processing and DTM quality assessment presented in this paper mainly the in-house developed computer programs have been used. The quality of DTM comprises its accuracy, density, and completeness. Different accuracy measures like RMSE, median, normalized median absolute deviation and their confidence interval, quantiles are computed. The completeness of the DTM is very often overlooked quality parameter, but when DTM is produced from the point cloud this should not be neglected as some areas might be very sparsely covered by points. The original density is presented with density plot or map. The completeness is presented by the map of point density and the map of distances between grid points and terrain points. The results in the test area show great potential of the DTM produced from UAS imagery, in the sense of detailed representation of the terrain as well as good height accuracy.
Highlights
Digital terrain model (DTM) is one of the main topographic classes and gives the digital representation of the bare terrain
The main focus of this paper is to present the approach to digital terrain model (DTM) quality assessment and to give a practical example on the test field data
This methodology has not been developed for the assessment of the quality of point clouds and DTMs produced from Unmanned Aerial System (UAS) imagery, but rather for “nationwide DTMs supporting orthoimage production of larger area project”, we found the potential to use this approach in UAS imagery originated digital terrain models
Summary
Digital terrain model (DTM) is one of the main topographic classes and gives the digital representation of the bare terrain. As the UASs are financially affordable for small enterprises, we are globally-wide witnessing an increasing use of the UAS for surveying purposes This is very positive, but there is a concern about the quality and reliability of the processed data. Different approaches to assess the capability and quality of UAS-based photogrammetric data collection and products can be found in publications. An approach to assess the accuracy of georeferenced point cloud of a natural coastal site with total station survey is presented in Harwin et al (2012). We would like to emphasise that the computer programs and algorithms used to accomplish this research project have been in-house developed
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