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Barber, Mills, Bryan 
40x40 degrees field of view. The system offers a precision of +/-4mm for the measurement of a single point at the one sigma level 
(Spanje, 2001). 
Both the Callidus and Riegl LMS-Z210 scanners use a mirror to deflect the laser in the vertical axis and mechanically rotate the 
scanner in the horizontal axis. This allows scanning up to a full 360 degrees for the Callidus and 340 degrees for the LMS-Z210. 
The precision of the Callidus system is quoted at +/-5mm for position measurement up to 32 meters, while the LMS-Z210 has a 
lower quoted precision of +/-25mm but at a range of up to 150meters for naturally reflecting targets. The Riegl LPM25HA 
mechanically scans the laser in both the vertical and horizontal planes and offers a quoted precision of +/-8mm in distance 
measurement (Spanje, 2001). 
The resolution of the scan is one of the parameters usually set before scanning. Resolution controls the number of points recorded in 
a scene and the level of detail visible in a scan. This parameter must be set for a particular range, if a scene has a large depth 
component the resolution must be selected for one of the distances. It may be necessary to rescan areas at the desired resolution. 
Toth and Grejner-Brzezinska (2000) discuss the sampling of surfaces for airborne LiDAR systems and the effect upon the 
representation of a surface; similar principles apply for terrestrial systems. 
Reflectance of materials is an issue for both triangulation and LiDAR scanners. If a material does not reflect the measurement beam 
sufficiently, data capture may not be possible. In some applications, especially the measurement of small objects with a triangulation 
scanner, the most desirable surface is matt white. This may be artificially introduced using chalk dust or a light coat of emulsion, 
however in some conservation projects this may be undesirable. Gordon et al., (2001) outline the response of a Cyrax 2400 scanner to 
red brick and mortar. Red brick was found to respond poorly to the scanner while the mortar provided a good response. As the 
reflectance characteristics of particular materials may prove to be important in some scanning projects, Gordon et al. suggest the 
production of spectral response libraries similar to those used in Remote Sensing, which may prove useful data in the application of 
scanning to different material types. 
3. PRACTICAL ISSUES 
It is worth considering the practicalities of laser scanning using large object laser scanners with a brief description of a generic 
system. Figure 3 shows a Cyrax 2400 system to illustrate a typical scanning system comprising of: 
• Scanner unit 
• Control unit 
• Power unit 
• Tripod and mount 
Control unit with shading 
Figure 3: An example scanner system - Cyrax 2400 
The scanner unit itself is generally larger than a traditional survey instrument and does not normally house the power source. Control 
is provided by a laptop computer, which can pose some problems when viewing the screen in bright sunlight. A sunscreen PC would 
be an ideal, if expensive, solution; good quality shading is otherwise the key. Power generally comes from a battery, in some cases a 
widely available 12v car battery allowing straightforward replacement in the event of a problem, in other cases a proprietary battery 
pack is supplied. This generally provides the power for the scanner but not the laptop control unit, so extra batteries for the laptop 
and some method of charging spent batteries may be required for a full day of scanning. In some cases the use of a portable 
generator may be more preferable. The scanner normally sits on a tripod, either of normal survey design or specially made. Some 
systems offer the option of a wheeled tripod, useful for interior scanning but impractical for use outdoors in rough/rocky areas. 
When LiDAR scanners first made an appearance, they realistically required two people to cope with the size, weight and number of 
boxes. New scanners now really require only one person, as equipment becomes lighter and more compact. The further 
rationalization of scanning systems will result in even smaller and lighter systems.