Fisheye Photogrammetry to Generate Low-Cost DTMS

Abstract

Abstract. In the archaeological practice, Digital Terrain Models (DTMs) and Digital Surface Models (DSMs) may be used to represent spatial information about the site by conveying information such as differences in levels, morphology of the terrain and movements of volumes during the excavation. Nowadays DTMs and DSMs can be easily obtained by image-based matching using low altitude aerial dataset acquired from a digital camera by means of a lifting device. In recent years, the spread of commercial multi-rotor unmanned aerial vehicles and their decreasing cost made low-altitude aerial photography even easier than before, where balloons, kites and telescopic masts would have been used instead. However, the use of drones is often forbidden by law, especially in the archaeological areas, and therefore a more traditional approach must to be adopted instead.This paper presents two different approaches adopted on the field to acquire the DTM of an archaeological excavation: the use of a pole held by a chest harness to lift a camera up to 3.5 m height fitted with a 20 mm wide angle lens; and a second solution that exploits ground-based fisheye photogrammetry. In general, an image network acquired from ground level is challenging due to: i) the poor coverage that can be obtained on the ground, ii) the large number of images that are required to cover large areas and consequently iii) the longer elaboration time that is required to process the data. The fisheye approach, however, proved to be more effective thanks to the more robust image network resulting both from the wider field of view and from the possibility to handle large datasets by downsampling the images and still retrieving strong key points. The main difference with the first system is that the monotonous images acquired by the 20 mm lens, very plain in texture, require working at full resolution in order to distinguish valid features in the sand.The final product of the tests carried out along this line in 2019 at Saqqara (Egypt) is a comprehensive DSM of the entire archaeological site with an accuracy of ~3 cm.

Analysis of the Photogrammetric Use of 360-Degree Cameras in Complex Heritage-Related Scenes: Case of the Necropolis of Qubbet el-Hawa (Aswan Egypt)

“…In these cases, the efficiency of data acquisition is one of the main aspects to be considered due to the difficulties in obtaining a complete coverage of the object by geomatic techniques that involve a large number of photographs (in the case of pinhole cameras) or scanning stations (in the case of using TLS). More specifically, in the case of photogrammetry, the number of photographs required to cover a complex scene can be reduced by using lenses that provide a larger Field of View (FoV), such as those using wide angle lenses [23][24][25][26][27], fisheye lenses [28][29][30][31][32][33][34][35][36][37][38] and 360-degree cameras [34,[39][40][41][42][43][44][45][46]. In this context, spherical photogrammetry [47] has undergone a great development recently using both fisheye images (FEI) and spherical images (SI), which are also known as panoramic images [47][48][49][50][51][52].…”

Multi-Sensor Geomatic Techniques for the 3D Documentation and Virtual Repositioning of Elements of the Church of S. Miguel (Jaén, Spain)

“…For this Heritage 2024, 7 2925 reason, some studies have recently focused on the improvement of this efficiency. Thus, some approaches have shown reductions in data acquisition work by increasing the field of view (FoV) of sensors, for example, in photogrammetry, through the use of wide-angle lenses [10][11][12][13][14], fisheye lenses [15][16][17][18][19][20][21][22][23][24], and 360-degree cameras [9,[25][26][27][28][29][30][31][32]. The recent use of fisheye images and panoramic images has made it possible to develop photogrammetric studies in complex scenes that had been almost impossible using conventional images.…”

Generation of a Multi-Scale Historic BIM-GIS with Digital Recording Tools and Geospatial Information

“…The paper describes the creation of the 3D digital environment based on multiple data, including data in situ captured with traditional digital recording tools (laser scanner and photogrammetry) and some innovative methods (spherical [20,21] and fisheye [22,23] photogrammetry).…”