LAUSR

While Eyre et al. (2016) have contributed some useful and interesting discussion with respect to the use of laser scanning as a method for measuring the consistency of stairway dimensions; they reach a different conclusion to Bowman et al. (2015). Eyre et al. concluded that ‘Owing to the errors associated with laser scanners, for precise high accuracy surveys to narrow tolerances such as the measurements of rise and goings outlined in this paper, laser scanning may not be the best survey methodology available’; and that ‘the classification of the error from laser scanning must be established, in order to consider if the error is relative and therefore can be mitigated, through further research’. Although Eyre et al. were planning ‘to explore the use of different laser scanning systems that may be better suited to the task of stair measurement’, we contend that they should have identified an appropriately accurate system prior to conducting their study and reaching an adverse conclusion. Determining the accuracy of laser scanning results is far more complex than that of simple linear measurements (Boehler and Marbs 2003), being a function of several characteristics that extend beyond the scanner itself, where the accuracy specifications published by laser scanner producers are not comparable, and should sometimes not be trusted. The Leica C10 laser scanner, which Eyre et al. used in case study 2, is marketed as an all-in-one laser scanner for any application representing the most capabilities and best value packed into a single instrument. It has a stated single point accuracy of ± 6 mm in 3D space, although it is capable of more robust returns and cleaner data on dark surfaces. The Leica HDS6000 laser scanner, used in case study 1, has a stated single point accuracy of ±4–6 mm in 3D space, depending on surface reflectivity and range. We consider the Eyre et al. laser scanning results probably contain at least ±3 mm scanner data noise. We believe engineering metrology laser scanners are required for ±1 mm accuracy. Furthermore, we suggest that the Eyre et al. data analysis approach was based on the standard manufacturer field survey procedure, not what was needed for accurate measurements of the stair dimensions. Specific comments on the Eyre et al. (2016) results