New Approach for Low-Cost TLS Target Measurement

The registration and calibration of data captured with terrestrial laser scanner (TLS) instruments can be effectively achieved using signalized targets comprising components of both high and low reflectivity, so-called contrast targets. For projects requiring tens or even hundreds of such targets, the cost of manufacturer-constructed targets can be prohibitive. Moreover, the details of proprietary target center coordinate measurement algorithms are often not available to users. This paper reports on the design of a low-cost contrast target using readily available materials and an accompanying center measurement algorithm. Their compatibility with real terrestrial laser scanner data was extensively tested on six different instruments: two FARO Focus three-dimensional (3D) scanners, a Leica HDS6100, a Leica P40, a RIEGL VZ-400, and a Zoller+Frohlich Imager 5010. Repeatability was examined as a function of range, incidence angle, sampling resolution, and target contrast. Performance in system self-calibration and from independent accuracy assessment is also reported. The results demonstrate compatibility for all five scanners. However, all data sets except the FARO Focus 3D require exclusion of observations made at high incidence angles in order to prevent range biases. Results also demonstrate that the spectral reflectivity of the target components is critical to ensure high contrast between target components, and therefore high-quality target center coordinate measurements.