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Abstract
The paper presents the results of testing a proposed image-based point clouds measuring method for geometric parameters determination of a railway track. The study was performed based on a configuration of digital images and reference control network. A DSLR (digital Single-Lens-Reflex) Nikon D5100 camera was used to acquire six digital images of the tested section of railway tracks. The dense point clouds and the 3D mesh model were generated with the use of two software systems, RealityCapture and PhotoScan, which have implemented different matching and 3D object reconstruction techniques: Multi-View Stereo and Semi-Global Matching, respectively. The study found that both applications could generate appropriate 3D models. Final meshes of 3D models were filtered with the MeshLab software. The CloudCompare application was used to determine the track gauge and cant for defined cross-sections, and the results obtained from point clouds by dense image matching techniques were compared with results of direct geodetic measurements. The obtained RMS difference in the horizontal (gauge) and vertical (cant) plane was RMS∆ < 0.45 mm. The achieved accuracy meets the accuracy condition of measurements and inspection of the rail tracks (error m < 1 mm), specified in the Polish branch railway instruction Id-14 (D-75) and the European technical norm EN 13848-4:2011.
Highlights
Non-invasive 3D measurement techniques in the railway sector use active and passive measurement methods
RealityCapture and Agisoft PhotoScan applications were used for processing on the RealityCapture and Agisoft PhotoScan applications were used for processing on the workstation workstation with the processor Intel® CoreTM i7-950 (8 MB Cache, 3.06 GHz), 24 GB RAM DDR3-1333 with the processor Intel®®CoreTM i7-950
Calculated RMS values are related to deviations on control points of the 3D model
Summary
Non-invasive 3D measurement techniques in the railway sector use active and passive measurement methods. In this scope of survey and inspections, mainly mobile systems are used, based on terrestrial laser scanning (TLS), which is often supported by sequences of digital images captured by video cameras (e.g., Lynx Mobile Mapper by Teledyne Optech Vaughan, Canada). The photogrammetric reconstruction of 3D objects is currently performed based on point clouds generated by dense image matching techniques. The dense point clouds and advanced data processing allow to recognize and completely reconstruct 3D objects, and to measure and extract geometric and semantic information [11].
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