The Laser scanner belongs to the new devices on the market of surveying instruments. Tests and measurements gave and still give information where a laser scanner can be used efficiently – partly better than a total station. The results of each measurement are calculated with the corresponding software of the producer or with the corresponding CAD or other surveying programs depending on the scanner.
The user cannot recognize which basis is used for the computation at most of the products. A conventional surveying program is not fit for a calculation with big amounts of data, which are the result of a laser scanner measurement. Programs shut down or becomes very slow, thus a processing of the data is impossible. Consequently, the data – the number of points – have to be reduced.
These aspects results in three questions, which where investigated in this study:
• Laser scanner versus total station: What is more accurate and what is more efficient?
• Do different software products result in equal outcomes?
• How far can a point cloud be reduced until there are changes in the result?
To answer these questions a pile of sand ( size around 400 m³ ) were surveyed twice: once with a laser scanner – Leica HDS 3000 – and once with a total station – Leica TPS1200. The data of the measurement were computed with three different software products: Geo, Geograf and Cyclone. Additional to this the point cloud was reduced stepwise and in each case, the volume was calculated. Thus, the effect of the reduction could be observed.
Between the different methods, no differences result in the accuracy and – in this investigation – hardly in the time for the measurement. The results of the computations showed that there is no difference between the programs Geo and Geograf. Just the result of Cyclone diverged from the other. The point cloud can be reduced without influences on the result with the order “Unify” until a point-to-point distance of 0,30 m.
Source: University of Gävle
Author: Pflipsen, Bettina