DSM Generation from Single and Cross-Sensor Multi-View Satellite Images Using the New Agisoft Metashape: The Case Studies of Trento and Matera (Italy)

Abstract

DSM generation from satellite imagery is a long-lasting issue and it has been addressed in several ways over the years; however, expert and users are continuously searching for simpler but accurate and reliable software solutions. One of the latest ones is provided by the commercial software Agisoft Metashape (since version 1.6), previously known as Photoscan, which joins other already available open-source and commercial software tools. The present work aims to quantify the potential of the new Agisoft Metashape satellite processing module, considering that to the best knowledge of the authors, only two papers have been published, but none considering cross-sensor imagery. Here we investigated two different case studies to evaluate the accuracy of the generated DSMs. The first dataset consists of a triplet of Pléiades images acquired over the area of Trento and the Adige valley (Northern Italy), which is characterized by a great variety in terms of geomorphology, land uses and land covers. The second consists of a triplet composed of a WorldView-3 stereo pair and a GeoEye-1 image, acquired over the city of Matera (Southern Italy), one of the oldest settlements in the world, with the worldwide famous area of Sassi and a very rugged morphology in the surroundings. First, we carried out the accuracy assessment using the RPCs supplied by the satellite companies as part of the image metadata. Then, we refined the RPCs with an original independent terrain technique able to supply a new set of RPCs, using a set of GCPs adequately distributed across the regions of interest. The DSMs were generated both in a stereo and multi-view (triplet) configuration. We assessed the accuracy and completeness of these DSMs through a comparison with proper references, i.e., DSMs obtained through LiDAR technology. The impact of the RPC refinement on the DSM accuracy is high, ranging from 20 to 40% in terms of LE90. After the RPC refinement, we achieved an average overall LE90 <5.0 m (Trento) and <4.0 m (Matera) for the stereo configuration, and <5.5 m (Trento) and <4.5 m (Matera) for the multi-view (triplet) configuration, with an increase of completeness in the range 5–15% with respect to stereo pairs. Finally, we analyzed the impact of land cover on the accuracy of the generated DSMs; results for three classes (urban, agricultural, forest and semi-natural areas) are also supplied.

CLARA WebGIS: Sharing Soil and Building Geophysical Data for Seismic Characterization of the City of Matera (Southern Italy)

“…In the framework of the CLARA project, we generated a DSM of the city of Matera and its surroundings, including the slope of the rocky ravine created by the Gravina stream [61]. In particular, we used the Agisoft Metahape photogrammetric software (Agisoft Metashape, 2021) [62] to process a cross-sensor multi-view satellite optical triplet composed of a WorldView-3 stereo pair and a GeoEye-1 image, whose acquisition features are described in [53].…”

“…We produced at first three DSMs using the three stereo pairs obtained by combining the three images. We followed the procedure described in [53] which adopts an original terrain-independent approach to refine the Rational Polynomial Coefficients (RPCs) supplied in each image metadata [63]. We applied the geoid undulations derived from the EGM2008 model [64] to transform the native ellipsoidal heights, derived from the RPC based orientation, to the corresponding orthometric ones.…”

“…We applied the geoid undulations derived from the EGM2008 model [64] to transform the native ellipsoidal heights, derived from the RPC based orientation, to the corresponding orthometric ones. Moreover, we cropped the DSMs considering the maximum intersection area common to the three DSMs and we resampled our products to 0.5 m. Lastly, we produced the final DSM computing a weighted mean of the three DSMs [53].…”

“…The increasing availability of new high-resolution optical spaceborne sensors allows to produce precise DSMs (such as the one included in the CLARA WebGIS) ensuring low cost, speed of data acquisition and processing, and relaxed logistic requirements [52]. For detailed presentation of the experimental design and the methodology adopted to produce the soil-building resonance map and to generate the DSM, the interested readers can refer to Gallipoli et al (2020) [8] and to Lastilla et al (2021) [53], respectively.…”

Sharing Soil and Building Geophysical Data for Seismic Characterization of Cities Using CLARA WebGIS: A Case Study of Matera (Southern Italy)

“…The increasing availability of new high-resolution optical spaceborne sensors allows for the creation of precise DSMs (such as the one included in the CLARA WebGIS), ensuring low cost, speed of data acquisition and processing, and relaxed logistic requirements [53]. A detailed presentation of the experimental design and the methodology adopted to produce the soil-building resonance map and to generate the DSM can be found in Gallipoli et al (2020) [8] and Lastilla et al (2021) [54], respectively.…”