CIPA 2003 XIX"' International Symposium, 30 September - 04 October, 2003, Antalya, Turkey 
and it is important that users are aware of the class of their 
instrument in the required classification. 
4.3 Data storage 
No specific data format or standardised set of metadata exists 
for TLS. It is not within the scope of this project to define a 
suitable format and supply the necessary management 
requirements. A brief overview of the issues involved 
however would benefit discussion of the topic. The LAS 
format (LAS, 2002) has recently been adopted by the ASPRS 
as a standard for airborne laser scanning (ALS). Although 
ALS and TLS share some common features and that the LAS 
format could be easily adapted to store TLS data it is 
suggested that a new format should be developed to ensure 
full compatibility with all future software systems. Any such 
format should be universally accepted by software 
developers and users. The following issues should be 
considered in any format definition: 
■ To maintain simplicity a single file should 
represent a single scan position (header files could 
be used to group together individual scans). 
■ Storing information in an arbitrary system would 
seem good practice but transformation parameters 
are also required so a single scan may be viewed 
together with other scans in a “real world” 
coordinate system. 
■ Support must be provided to store intensity and/or 
RGB values for each point. 
■ Optimum compression of the data should be 
possible. The data volumes provided by the 
available systems vary, with the Z+F Imager 5003 
providing up to 1GB from a single scan position. 
A compressed binary format is therefore 
preferable. 
As no format is currently available it has been necessary to 
adapt the specification to allow for a variety of formats with 
the emphasis being placed on the ability to transfer data 
between software systems. The transfer of data between 
software systems would be best facilitated through the 
application of a standard level of metadata, both for 
individual scans and for a project as a whole. For raw scan 
data the specification requires the following metadata: 
■ Total number of points 
■ Point spacing on the object 
■ Filename for control data 
■ Weather during survey 
■ The file name of an image, located at the point of 
collection, showing the data collected 
This metadata should be contained in a digital file and in 
hard copy in the post survey report. The post survey report 
should also include the standard requirements found in the 
current metric survey specification such as details of control 
point coordinates and accuracies. 
Although the generation of this information may at first seem 
like additional work for the contractor it is envisaged that in 
future all metadata would be generated semi-automatically. 
Most systems for manipulating and processing scan data now 
accepted control and image data in addition to scan data. 
This could also be extended to contain notes and sketches. 
Such data management systems (DMS) would make 
metadata generation easier and in the long term these DMS 
may become full GIS systems which advanced 3D spatial 
data analysis tools. Such DMS may even become actual 
deliverables themselves. 
It is common to find users stating that decimation of data was 
required before any viewing/processing could be performed. 
It may be necessary to define appropriate decimation 
procedures to allow for this if required. As the standard 
computer specification increases the impact of this limitation 
maybe reduced. 
4.4 Common faults 
Finally the specification aims to limit some of the common 
faults of laser scanning surveys. These include: 
■ Data voids - These are normally caused by 
temporary/permanent occlusions of the 
measurement beam by vehicle or pedestrian traffic 
(Figure 3) or obstruction by the building itself. 
Where it is not possible to prevent such occlusions 
it will be necessary to provide sufficient overlap 
between scans to fill such voids. 
■ File name of the raw data 
■ Date of capture 
■ Scanning system used (with serial number) 
■ Company name 
■ Monument name 
■ Monument number (if known) 
■ Survey number (if known) 
■ Scan number (unique scan number for this survey)