Comparison of Time-of-Flight and Phase-Shift TLS Intensity Data for the Diagnostics Measurements of Buildings

Abstract

In recent years, the terrestrial laser scanning system (TLS) has become one of the most popular remote and nondestructive testing (NDT) methods for diagnostic measurements of buildings and structures as well as for the assessment of architectural heritage. Apart from 3D coordinates, the power of a laser beam backscattered from the scanned object can be captured by TLS. The radiometric information of the point cloud, called “intensity”, can provide information about changes in the physio–chemical properties of the scanned surface. This intensity can be effectively used to detect defects in the surfaces of walls, such as cracks and cavities, moisture, biodeterioration (mosses and lichens) or weathered parts of the wall. Manufacturers of TLS mainly use two different principles for distance measurement, time-of-flight (TOF) and phase-shift (PS). The power of energy in both types of rangefinders might be absorbed or reflected in a slightly different way and provide more or less detailed radiometric point cloud information. The main aim of this investigation is to compare TOF and PS scanners in the context of using TLS intensity data for the diagnostics of buildings and other structures. The potential of TLS intensity data for detecting defects in building walls has been tested on multiple samples by two TOF (Riegl VZ400i, Leica ScanStation C10) and two PS (Z + F 5016 IMAGER, Faro Focus3D) scanners.

A Case Study of Deformation Measurements of Istanbul Land Walls via Terrestrial Laser Scanning

“…Unlike scanners based on time-to-flight principle, where distance measurement consists of measuring the time between emitted and reflected laser pulse, the phase-based scanners measure the phase-shift of a pulse and distance to the object is calculated along sinusoidally modulated laser pulse. Several studies, for example [42] and [43], have been carried out to compare these types of scanners and TLS based on phase-shift distance measurement proved to be better instrument for surveying.…”

Investigating the barriers to laser scanning implementation in building refurbishment

“…Currently, terrestrial LS is one of the most common methods for gathering as-built data of existing buildings (Becker et al, 2019;Dore and Murphy, 2017;Suchocki, 2020) due to the high accuracy and point density that the technique provides (Abdul Shukor et al, 2015;Alomari et al, 2016;Cheng et al, 2015;Han, 2012;Hong et al, 2015;Lee et al, 2015;Sepasgozar et al, 2015;Shanbari et al, 2016;Volk et al, 2014). A terrestrial laser scanner captures the geometry and textual information of an existing building by automatically recording millions of 3D points (Dore and Murphy, 2017;Rocha et al, 2020).…”

“…Laser scanners mainly use one of three different principles for measurements: triangulation, time-of-flight (ToF), or phase-comparison. Even though all of these methods produce a 3D point cloud, the range and accuracy of registered values vary between these methods (Dore and Murphy, 2017;Historic England, 2018;Suchocki, 2020). Typically, laser scanners operated by ToF or phase are used in the recording of building exteriors and interiors (Historic England, 2018).…”

The Quality Assessment of Different Geolocalisation Methods for a Sensor System to Monitor Structural Health of Monumental Objects

“…The result of such measurement is a 3D point cloud representing the shape of measured objects together with the intensity of the returning signal which may be successfully applied in examination of properties of investigated objects [46] such as their reflectance, roughness, moisture, brightness, and grain size [47,48]. However, in the case of geolocalisation purposes, the significant factors are measurement accuracy and resolution.…”