# Improvements in Rock Mass Description for Stope Design by Geophysical and Geochemical Methods
## 6 Photogrammetric Scanning for Rapid Geometrical Characterization
### Methodology  
Three different approaches to capture the images were tested. First, the method was demonstrated in a 10 m-long tunnel section of granitic rock, which was captured with a 360-degree camera (Figure 10a). The camera takes six photos at the same time, which increases the acquisition speed. Pictures were taken from 27 locations (Figure 10c) and a 3D model was reconstructed using SfM-MVS photogrammetry. To enable fracture orientation measurements, the model was oriented using an orientation board with the control points proposed in [47]. The resulting model was then compared with a reference laser scan and a more conventional digital single-lens reflex (DSLR) camera-based model. The 360 camera-based model was then used to remotely map rock mass properties. The mean orientation of three identified discontinuity sets was measured from the point cloud using a semi-automatic clustering-based method [48].  
The second acquisition method for rapid photogrammetry was based on a multi-camera rig, which offers advantages over traditional methods in terms of time and cost efficiency. A multi-camera rig with four GoPro Hero 8 cameras was designed to quickly cap  
Figure 9: Cumulative plot of the differences between the GPR and photogrammetric models of the fracture surfaces, all scan lines. (**Left**): differences observed with the initial calibration based on the median of the measured dielectric permittivity values, representative of the general performance of the method. (**Right**): differences after a constant shift in all GPR values by the prior median difference rounded to 1 mm, representative of the performance with respect to small-scale variation in the geometry.  
ture images of the tunnel surface (Figure 11b). The method was tested at the Underground Research Laboratory of Aalto University (URLA), where a tunnel drift was digitized using the multi-camera rig and a portable lighting setup (Figure 11a). Data were acquired by recording 4K videos with each camera, with frames extracted at 1 s intervals. The frames were processed using RealityCapture photogrammetric software v1.2, resulting in a 3D model and a point cloud. Reference distance measurements on the 3D model showed a mean error of 3.7 mm and a maximum error of 8.6 mm. Discontinuity orientation measurements were obtained using the computer-assisted remote mapping method with the Compass plugin in CloudCompare software v2.12.0 [49] and the semi-automatic method in Discontinuity Set Extractor (DSE) software v3.01 [48]. In addition, reference fracture orientation measurements were taken manually using a geological compass and compared with the remote measurements.  
Finally, UAV (drone) photogrammetry was explored as a third rapid method for rock mass characterization in underground excavations, particularly for stope design. For this purpose, an open drone image dataset [50] consisting of 2105 images recorded inside a stope in the Golden Sunlight Mine in Montana, USA, were processed. The 3D stope model was reconstructed photogrammetrically, and discontinuity mapping was then performed using a semi-automatic approach to identify rock discontinuities and measure their orientation (Figure 12).  
Figure 10: Photogrammetric scanning of an underground tunnel with a 360-degree camera (**a**). The 3D model (**b**) was produced from a series of images captured at 27 locations (**c**). The discontinuity sets were extracted from the 3D models using a semi-automatic method by [48] (**d**,**e**) with three discontinuity sets: J1 = blue, J2 = green, J3 = red, and compared with conventional geological compass measurements (**f**) (modified after [51]).