The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B5. Beijing 2008 
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Laser beam modulation lengths 
1.2, 9.6 and 76.8 m 
Points per second 
120 000 
Maximum distance 
70 m 
Linearity error at 10 m 
3 mm 
Vertical Field of View 
320° 
Horizontal Field of View 
360° 
Laser wavelength 
785 nm 
Laser power 
22 mW 
3. MEASUREMENTS 
The target sled was moved along the barline in a straight line at 
certain distance intervals, and distance measurements were 
made to measurement targets with both instruments from 
opposite directions. A steel measuring rod was used to guide the 
sled along a straight line. The straight line on top of the bar was 
measured and marked before the calibration by using the Leica 
TCA2003 tacheometer. 
Table 1. Technical data of Faro LS 880HE80 (Faro, 2005; 
Lichti and Licht, 2006) 
2.2 Reference equipment 
The reference equipment used was Leica TCA2003 robot 
tacheometer (S.No. 438743) (Figure 1 b), which can track the 
motion of the prism. The distance measuring uncertainty is 1 
mm + 1 ppm and the angle measuring accuracy is 0.15 mgon 
(Leica, 2003). Regarding that information, the ranging accuracy 
of the tacheometer was expected to be a degree better than that 
FARO LS could produce, and could thus provide appropriate 
reference for calibration 
An ordinary Leica round prism (GPR1) was used as target in 
the tacheometer measurements. TCA2003 uses phase 
measurement of a modulated infrared laser beam in its range 
determination algorithm. Tacheometer provides automatic 
target recognition (ATR). 
2.3 Other arrangements 
The tested laserscanner Faro LS 880 HE80 was placed on a 
platform at the end of the about 80 meters long barline 
(Figure 4) and a reference equipment, a calibrated tacheometer 
Leica TCA2003, was placed on the platform at the other end. 
These instrument platforms were permanently mounted at both 
ends of the barline. 
In the calibration phase, the first range measurements were 
made at a distance of about 1 m from the laser scanner. The 
target sled was then moved with approximately 10 cm distance 
intervals from the 1 m distance up to 5 m to reveal the 
phenomena in the shortest 1.2 m modulation wavelength, and 
also, due to the limited length of the steel rod guide, with 
approximately 45 cm intervals for distances from 5 m up to 
about 30 m from the scanner. The distances observed for the 
first target location with both instruments were used as 
reference distances d 0 ,L and d 0 j for the other measurements. 
Figure 4. Measurement at a first distance about 1 m from the 
laser scanner. The tubular level that was used for levelling the 
sled is also shown in the image. Circles seen on the wall were 
not used in this calibration. 
Measurement targets for both instruments were placed on a 
specially manufactured “target sled” seen in Figure 4. The sled 
has levelling screws, and tribrach adapters were tightly attached 
to the sled. Both measurement targets were attached to tribrachs 
on the sled. The centers of the two tribrach adapters on the sled 
were 14.9 cm apart. 
The scanner target used for the calibration (see Figure 3 b) was 
made of a 5 mm thick aluminum plate with a target pattern 
printed on a piece of plain sticker paper. The target pattern had 
triangular shapes pointing towards the target center to provide 
reliable determination of the target center even at large 
distances. The target center was approximated from the laser 
data using the intensity image produced by the scanner. 
Figure 3. (a) The calibration barline used in the measurements, 
(b) Scanner target mounted on the prismholder. 
The carrier sled and prisms were accurately levelled at the sled 
location for the first distance using tubular levels. Subsequently, 
at each distance step along the bar line, the sled was levelled 
using a separate tubular level. Four single distance 
measurements were taken for each distance with both the laser 
scanner and tacheometer. 
From the laser scanner data the target center was first 
determined using the intensity image of the data provided by the 
scanner, and then four closest distance recordings around the 
target center were used as calibration observations. That would 
result in a small uncertainty in relation to the exact target center 
location as a function of the angular resolution used for the 
scanning, but no significant effect to the distance (e.g ~1.5pm 
range error at 30 m distance for 0.018° (0.3 mrad) angular 
resolution). 
The tacheometer provided directly horisontal distances between 
its origin and the targeted prism. Measurements were made 
either by using ATR or maximum signal of the prism was found 
manually. A precision distance measuring mode was used and 
four single measurements corrected for athmospheric effects 
were made at each measured distance. 
The mean of the four tacheometer and TLS measurements for 
each target distance and distance differences for the 
observations were calculated. For both instruments, the result 
(mean value) of the measurements at the first distance was 
subtracted from the results of the measurements for the rest of