The Effect of Surface Material on Cylinder Point Clouds

The aims of the experiment described in this article are to analyse the effect of material differences and the highly curved surface of small cylinders on laser scanning data uncertainty, and to link the experimental results to theory. To this end, seven cylinders with different surface properties were measured with a terrestrial laser scanner. The cylinders were chosen to represent materials common in the built and natural environments, in addition to having distinct reflectivity characteristics. The cylinders are purposefully chosen to be small relative to the resolution and beamwidth, as this has proven to be a difficult geometry reconstruction problem. As the true cylinder locations are known, the incidence angle, cylinder distance and propagation error are quantified for each point. For an ideally reflective surface, theory dictates a Gaussian propagation error and such a distribution type is commonly used for quantifying laser scanning uncertainty. This study however found it to have worse predictive power than a simple triangular distribution. Additionally, introducing material-dependence through scaling the uncertainty by intensity did not consistently improve the results. This study further found the data to be poorly suitable for least-squares cylinder fitting due to its bias and heteroscedasticity and found biased geometry comparable to that of previous studies for cylinders of small diameters.