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Field comparison of pulse-based and phase-based laser scanners for civil engineering applications

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Abstract
Laser scanning is more and more being applied in different fields of applications, including civil engineering. However, when considering pulse-based and phase-based laser scanners, there are important differences that have an influence on the choice of the most suited type of laser scanner, depending on the project's specifications and the accuracy requirements. Aspects that can be assessed are the horizontal and vertical angle error, range error, noise on the distance measurement, spot size, achievable point resolution etc. Moreover, the reflectance properties of the object's material also have an important influence on the accuracy of the resulting point cloud. When including a more economical factor, the field of view, the scanning speed and maximal range play a significant role. Notwithstanding the need for a comparison between different types of measurement instruments before starting a project, the manufacturer's specifications are not sufficient to thoroughly decide which type of laser scanner is the most suited for a specific project. The manufacturer's specifications are determined in laboratory conditions and mostly a systematic and standardized definition of the accuracy, e.g. in accordance with an internationally accepted protocol, is not present. Several uniform methodologies to assess the accuracy of different types of laser scanners already exist, but most of these methodologies are based on laboratory measurements, providing no answer to the question how the measurement instrument will perform in actual field conditions. The research described in this paper handles a comparison between pulse-based and phase-based laser scanners for civil engineering applications, based on field measurements. For the comparison, measurements with a Leica HDS6100 (phase-based) laser scanner, a Leica C10 (pulse-based) and a Leica ScanStation 2 (pulse-based) laser scanner are used. Not only the accuracy, but also the edge effects and the achievable resolution are assessed. Furthermore, the influence of different types of commonly used construction materials on the accuracy is compared. Based on the measurements of several flat reference targets, the results indicate no significant difference in 3D accuracy between the tested pulse-based and phase-based laser scanners. When using spherical targets, significant differences can be observed. The phase-based laser scanner results in a finer achievable resolution at short distances (e.g. tested on 6 m), where the pulse-based laser scanner delivers better results at longer distances (e.g. tested on 22 m). The tested edge effects show no significant differences between both types of laser scanners. Furthermore, the measurements indicate that the pulse-based laser scanner results in lower noise levels for the different tested construction materials. This research delivers more insights in the performance of laser scanning instruments in real measurement conditions, allowing to more profoundly choose the most suited type of laser scanner for each project.
Keywords
accuracy assessment, laser scanning, field experiments, calibration, comparison

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Chicago
Nuttens, Timothy, Cornelis Stal, Jasper Wisbecq, Greta Deruyter, and Alain De Wulf. 2014. “Field Comparison of Pulse-based and Phase-based Laser Scanners for Civil Engineering Applications.” In International Multidisciplinary Scientific GeoConference-SGEM, 169–176.
APA
Nuttens, T., Stal, C., Wisbecq, J., Deruyter, G., & De Wulf, A. (2014). Field comparison of pulse-based and phase-based laser scanners for civil engineering applications. International Multidisciplinary Scientific GeoConference-SGEM (pp. 169–176). Presented at the 14th International Multidisciplinary Scientific Geoconference (SGEM).
Vancouver
1.
Nuttens T, Stal C, Wisbecq J, Deruyter G, De Wulf A. Field comparison of pulse-based and phase-based laser scanners for civil engineering applications. International Multidisciplinary Scientific GeoConference-SGEM. 2014. p. 169–76.
MLA
Nuttens, Timothy, Cornelis Stal, Jasper Wisbecq, et al. “Field Comparison of Pulse-based and Phase-based Laser Scanners for Civil Engineering Applications.” International Multidisciplinary Scientific GeoConference-SGEM. 2014. 169–176. Print.
@inproceedings{7173895,
  abstract     = {Laser scanning is more and more being applied in different fields of applications, including civil engineering. However, when considering pulse-based and phase-based laser scanners, there are important differences that have an influence on the choice of the most suited type of laser scanner, depending on the project's specifications and the accuracy requirements. Aspects that can be assessed are the horizontal and vertical angle error, range error, noise on the distance measurement, spot size, achievable point resolution etc. Moreover, the reflectance properties of the object's material also have an important influence on the accuracy of the resulting point cloud. When including a more economical factor, the field of view, the scanning speed and maximal range play a significant role. 

Notwithstanding the need for a comparison between different types of measurement instruments before starting a project, the manufacturer's specifications are not sufficient to thoroughly decide which type of laser scanner is the most suited for a specific project. The manufacturer's specifications are determined in laboratory conditions and mostly a systematic and standardized definition of the accuracy, e.g. in accordance with an internationally accepted protocol, is not present. Several uniform methodologies to assess the accuracy of different types of laser scanners already exist, but most of these methodologies are based on laboratory measurements, providing no answer to the question how the measurement instrument will perform in actual field conditions. 

The research described in this paper handles a comparison between pulse-based and phase-based laser scanners for civil engineering applications, based on field measurements. For the comparison, measurements with a Leica HDS6100 (phase-based) laser scanner, a Leica C10 (pulse-based) and a Leica ScanStation 2 (pulse-based) laser scanner are used. Not only the accuracy, but also the edge effects and the achievable resolution are assessed. Furthermore, the influence of different types of commonly used construction materials on the accuracy is compared. 

Based on the measurements of several flat reference targets, the results indicate no significant difference in 3D accuracy between the tested pulse-based and phase-based laser scanners. When using spherical targets, significant differences can be observed. The phase-based laser scanner results in a finer achievable resolution at short distances (e.g. tested on 6 m), where the pulse-based laser scanner delivers better results at longer distances (e.g. tested on 22 m). The tested edge effects show no significant differences between both types of laser scanners. Furthermore, the measurements indicate that the pulse-based laser scanner results in lower noise levels for the different tested construction materials. 

This research delivers more insights in the performance of laser scanning instruments in real measurement conditions, allowing to more profoundly choose the most suited type of laser scanner for each project.},
  author       = {Nuttens, Timothy and Stal, Cornelis and Wisbecq, Jasper and Deruyter, Greta and De Wulf, Alain},
  booktitle    = {International Multidisciplinary Scientific GeoConference-SGEM},
  isbn         = {978-619-7105-12-4},
  issn         = {1314-2704},
  keyword      = {accuracy assessment,laser scanning,field experiments,calibration,comparison},
  language     = {eng},
  location     = {Albena, BULGARIA},
  pages        = {169--176},
  title        = {Field comparison of pulse-based and phase-based laser scanners for civil engineering applications},
  year         = {2014},
}

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