Abstract
Abstract. The evolution of Structure from Motion (SfM) techniques and their integration with the established procedures of classic stereoscopic photogrammetric survey have provided a very effective tool for the production of three-dimensional textured models. Such models are not only aesthetically pleasing but can also contain metric information, the quality of which depends on both survey type and applied processing methodologies. An open research topic in this area refers to checking attainable accuracy levels. The knowledge of such accuracy is essential, especially in the integration of models obtained through SfM with other models derived from different sensors or methods (laser scanning, classic photogrammetry ...). Accuracy checks may be conducted by either comparing SfM models against a reference one or measuring the deviation of control points identified on models and measured with classic topographic instrumentation and methodologies. This paper presents an analysis of attainable accuracy levels, according to different approaches of survey and data processing. For this purpose, a survey of the Church of San Miniato in Marcianella (Pisa, Italy), has been used. The dataset is an integration of laser scanning with terrestrial and UAV-borne photogrammetric surveys; in addition, a high precision topographic network was established for the specific purpose. In particular, laser scanning has been used for the interior and the exterior of the church, with the exclusion of the roof, while UAVs have been used for the photogrammetric survey of both roof, with horizontal strips, and façade, with vertical strips.
Highlights
The evolution of Structure from Motion (SfM) techniques and their integration with the established procedures of classic stereoscopic photogrammetric survey have provided a very effective tool for the production of three-dimensional textured models
Analysis of the results show that RMSE values are virtually constant throughout the variation of Ground Control Points (GCPs) number, for both Free Net and Constrained processing, ranging from 3 to 5 Ground Sampling Distance (GSD) and from 2 to 4 GSDs respectively
It can be concluded that this particular case of virtually planar surface does not yield deviations of any significance depending on GCP number and processing mode
Summary
The evolution of Structure from Motion (SfM) techniques and their integration with the established procedures of classic stereoscopic photogrammetric survey have provided a very effective tool for the production of three-dimensional textured models. The use of multi-rotor systems allows achieving both horizontal and vertical photogrammetric strips in close proximity to the survey objects Several software offerings, both commercial and open source, are available for automatic processing of these strips, allowing, with comparative ease, to derive three-dimensional models from collections of images. Both commercial and open source, are available for automatic processing of these strips, allowing, with comparative ease, to derive three-dimensional models from collections of images Such models are aesthetically pleasing but can contain metric information, the quality of which depends on several factors: photo capturing strategies, instruments, metric accuracy and surveying methodologies for ground geometric references (control points), geometric resolution and radiometric quality of images and applied processing methodologies. UAV-based surveying requires just a few thousands euros in order to purchase aircraft, photographic sensor and processing software as an entry level kit, so that potential users are numerous and with vast cultural differences
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