CIVIL ENGINEERING & CONSTRUCTION
Malcolm Donald, director of Plowman Craven Limited, explains the advantages of laser scanning on rail projects. N
etwork Rail’s ‘right first time’ philoso- phy has led to wide-ranging accept-
ance of the benefits of using 3D laser scan- ning for capturing survey measurement data for rail related projects.
The need for survey data at the start of any project is essential to the design process; capturing it is inevitably controlled by the access available to survey teams working within restricted time periods on the UK’s busy rail network.
Laser scanners, the latest now capable of measuring up to 1 million co-ordinated points per second,
enable survey
companies to work within these short time periods and yet capture enough data to progress the early stages of a project’s critical path.
Behind all laser scanning data capture there is a framework of high-precision survey control established by the survey company, without which the scan data is unusable. It is the experience of working with laser scanners, aligned with good survey prac- tice and quality control procedures, which ensures the client receives the data to the standards required and to programme.
Continuous development of the ‘scan’ prod- uct has resulted in the addition of high dy- namic range photography (HDR) into the scan-cloud, enabling the end user to navi- gate through, zoom into, investigate and measure information gathered from the collected data. This is facilitated through a web-based free viewer via a workstation or laptop. A query relating to a particular site can often be resolved by ‘visiting’ the site via the computer screen and extracting a dimension – no access restrictions ap- ply and the design process can continue to schedule. This new approach to data pres- entation has been received enthusiastically in all quarters (see figure 1).
London stations which have benefitted from 3D laser scanning include: Paddington, Kings Cross, Victoria,
Farringdon and
London Bridge. Crossrail, for instance, required precision scanning with HDR as the deliverable for its Paddington ‘box’ in which listed building MacMillan House had to be incorporated into the design. A bespoke approach to the 3D model was devised which met the requirements of both Crossrail and English Heritage (see figure 2).
40 | rail technology magazine Aug/Sep 11
From the laser scan point cloud, all data required for design can be extracted in the form of 2D information such as floor plans, elevations and sections. Increasingly, cli- ents require complex 3D models to design with. These models lend themselves to the phasing of projects and to resolving issues with existing infrastructure, particularly where above and below ground interfaces, local services and even main trunk sewers exist. High accuracy surveying gives con- fidence that the model viewed is ‘as-built’, thus providing the base upon which pro- jects can be designed.
London Bridge Station, the ‘Jewel in the Crown’ of the £5bn Thameslink Pro- gramme, will undergo major reconstruc- tion works after the 2012 Olympic Games. Design and planning will be based on a two-year survey programme which has seen every corner of the complex arched structure of the station laser scanned, with HDR photography added.
Nearly 2,000 scans, collecting 3Tb of data, have provided the measurement database for the modelling and subsequent design of the station. The farsighted approach of the Thameslink team, which has advocated
the use of scanners throughout the pro- ject, now see point clouds and 3D models as part of the standard toolset available to designers in Network Rail.
The use of laser scanning and 3D model- ling is bringing value added surveying to the rail industry. Those companies willing to invest in the latest technology and in developing their teams in advanced CAD processing, will ensure the industry has the data it requires for validation, design and planning for its projects; value added, pre- cise and right first time.
The Plowman Craven name is associated with high quality and innovation, delivering professional surveying services to a wide ranging customer base. With over 30 quali- fied surveyors and an experienced manage- ment team, Plowman Craven has been the chosen surveyor on some of the UK’s most recent prestigious rail-related projects.
FOR MORE INFORMATION
141 Lower Luton Road, Harpenden, Herts. AL5 5EQ T: 01582 765566 / 0797 791 6877 / 020 7490 7700 E:
mdonald@plowmancraven.co.uk W:
www.plowmancraven.co.uk
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