The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B5. Beijing 2008 
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Distance ~ 14m 
◄ 
Laser scanner 
Trimble®GX 
Figure 1. Principle of the test configuration 
3. TEST CONFIGURATION AND TEST BOARDS 
For the investigation of the effects of object materials and 
colours on laser scan measurements special test boards had been 
constructed where several test plates of different materials were 
mounted. Figure 1 illustrates the configuration of the tests. It 
has to be taken into account that the board under investigation 
had been positioned in the centre, in order that the laser rays hit 
the board orthogonal. The distance of 14 m had been chosen 
due to a typical range for building acquisition. All main 
investigations have been carried out at day and night-time to 
estimate the influences of surrounding lighting conditions. 
To analyse the accuracy of the range measurements an adjusted 
plane (best fit) has been calculated for all laser points of the 
same plate and the mean square error (MSE) was derived based 
on the point distances (residuals) to this plane. For the analysis 
of the recorded intensities the mean value has been computed. 
Figure 2. Colour sheets red, green, blue, 
light red, light green, light blue 
4. ANALYSIS OF GREY SCALED AND COLOURED 
MATERIALS 
In order to test the effects of different grey levels of an object 
on the laser scan measurements, several sheets with b/w 
patterns and a sheet with a grey wedge was used. To assess the 
quality of measurements on coloured surfaces, four sheets in 
red, green, blue and black had been mounted on the main board. 
Also three sheets in light red, light .green and light blue were 
supplemented (Figure 2). 
4.1 Geometric accuracy 
The range measurements on our grey scaled test sheets have 
proven a significant dependence between the brightness of the 
object and the obtained accuracy and therefore, confirm 
previous results of other research groups (e.g. Hanke et al., 
2006). Figure 3 shows the results of the recording of the grey 
wedge. For dark areas an error of about MSE = ± 5 mm and 
about MSE = ± 2.5 mm for bright parts was estimated. 
Unexpectedly the MSE value for white is a little bit higher than 
the minimum at green (colour of laser light). 
The analysis of the colour sheets leads to similar results, i.e. the 
range errors decrease from black over red, blue and green 
(colour of the laser light) to the light colours. Again the MSE 
value for white is higher than the minimum of the light coloured 
sheets. Besides this the most significant feature is the enormous 
difference between measurements at day and night-time (approx, 
a factor of 2). So the range error for black lies about MSE = ± 
5.1 mm at daytime and about MSE = ± 2.4 mm at night-time. 
These values decrease to the light colours with a MSE of about 
± 2.2 mm (daytime) and MSE = ± 1.4 mm (night-time) (Figure 
4). Again the MSE for the white sheet lies above the minima 
with only a slight difference between night and day.