C/PA 2003 XIX th International Symposium, 30 September - 04 October, 2003, Antalya, Turkey 
helping to provide experience and understanding of the type 
of large scale survey that may, in the future, be performed 
using TLS. It also provided a basis from which to address 
important data management issues. A total of 43 scans were 
collected using a Cyrax 2500 TLS and over 50 control points 
were used to register data to the local site grid. To ensure the 
independence of the specification document from any one 
particular system three different scanning systems were used. 
In addition to the Cyrax 2500, a Zoller and Froelich Imager 
5003 system was used to scan the presbytery (22 m x 14 m x 
22 m in size) and, during the second survey, a Riegl LMS 
Z320 system was used to scan several areas of the church. 
Figure 1. The remains of the Priory Church (solid 
shading represents standing walls) Hadcock, 1991. 
The third survey will validate the specification document by 
undertaking a “commercial’’ survey. A project brief will be 
defined by English Heritage prior to the survey and data then 
collected to the level described in the specification. The 
survey data will then be delivered to English Heritage for 
assessment and comment. 
4. DISCUSSION 
The following discussion is based on the data collected 
during the first and second surveys in addition to consultation 
with the steering committee. It outlines some of the 
requirements and issues of the specification and illustrates 
this with examples from the first two surveys. 
4.1 Definitions 
In order to ensure clarity throughout the specification 
document a list of definitions was provided. A selection of 
these definitions are provided below: 
■ Data voids - Sections within the point cloud, more 
than twice the point density of the scan in size, 
which contain no data despite surface information 
on the object itself. 
■ Peripheral data - Additional scan data collected 
during the scanning process not explicitly defined 
as being required in the project brief. 
■ Point cloud - A collection of XYZ coordinates in a 
common coordinate system that portrays to the 
viewer an understanding of the spatial distribution 
of a subject. It may also include intensity or colour 
information. Generally a point cloud contains a 
relatively large number of coordinates in 
comparison with the volume the cloud occupies. 
■ Point density - The average distance between XYZ 
coordinates in a point cloud. Density can be 
represented by either a horizontal and vertical 
separation taken from/to the centre of the footprint 
at a specified range, or by using angular values. 
■ Registration - The process of determining the 
transformation parameters required to transform 
point clouds onto a common coordinate system. 
■ Resolution - The smallest discernable unit of 
measurement. 
■ Scan orientation - The approximate direction in 
which the scan is made if the system does not 
provide a 360 degrees field of view. 
■ Scan origin - The origin of the arbitrary coordinate 
system in which scans are performed. When the 
scan origin is transformed onto the site coordinate 
system it becomes the scan position. 
■ Scan position - The location, in a known coordinate 
system, from which a single scan is performed. If 
the system does not perform a full 360 degree scan, 
several scans may be taken from the same scan 
position, but with different scan orientations. 
■ Scanning artefacts - Irregularities within a scan 
scene that are a result of the scanning process 
rather than features on subject itself. These may be 
geometric or radiometric in nature. 
■ Terrestrial laser scanning system (TLS) - Any 
ground based device that uses a laser to measure 
the three-dimensional coordinates of a given region 
of an objects surface automatically, in a systematic 
order at a high rate in (near) real time (adapted 
from Boehler and Marbs, 2002). 
4.2 Data capture 
Before any survey takes place the contractor must supply a 
method statement detailing the techniques to be used. In the 
case of TLS this must show the area to be scanned along with 
details showing that the scanning system to be used is 
operating correctly. It is considered vital that, for QA 
purposes, such information is provided. However, as the 
majority of manufacturers do not provide calibration 
certificates some other standard is required. Details of a test 
showing the system is operating to its supplied level of 
precision and accuracy are required, although, as the exact 
nature of such a test is likely to vary between users the 
ultimate responsibility should be on the client to ensure 
appropriate information is provided. 
Accuracy in the recording of cultural heritage consists of 
geometric accuracy, the closeness of a coordinate to its true 
value, and narrative accuracy the “correctness” of a 
particular attribute. From discussion with end users it was 
clear that each type of accuracy must be specified for. In 
TLS the two most important parameters for this are the 
chosen point density and the geometric accuracy of the point 
measurement. It is necessary to determine suitable values for 
both. It is possible to assume that point density is mainly