3D Laser Scanning Surveys
Laser scanning is a relatively new technique for surveyors to use in solving a host of measurement problems.

As a survey technique, it is extremely powerful for the rapid capture of massive amounts of positional data in full 3D on your site grid. However, we are here to offer best advice, and for some projects, we will highlight that scanning is one tool in the surveyor’s toolbox. It may be more appropriate to use a tape or level and staff to acquire your data.

How does it work?

We use a time-of-flight 3D laser scanner which uses laser light to probe the subject with a laser range finder. A laser is used to emit a pulse of light and the amount of time before the reflected light is seen by a detector is timed. Since the speed of light is a known, the round-trip time determines the travel distance of the light, which is twice the distance between the scanner and the surface.

The accuracy of a time-of-flight 3D laser scanner depends on how precisely we can measure the time (approximately 3.3 picoseconds is the time taken for light to travel 1 millimetre).

The laser range finder only detects the distance of one point in its direction of view. Thus, the scanner scans its entire field of view one point at a time by changing the range finder’s direction of view to scan different points. The view direction of the laser range finder can be changed by either rotating the range finder itself, or by using a system of rotating mirrors. The latter method is commonly used because mirrors are much lighter and can thus be rotated much faster and with greater accuracy. Typical time-of-flight 3D laser scanners can measure the distance of 10,000 to 100,000 points every second.

Click here for the simpler animated explanation….

The 3D points observed are grouped together as a ‘point cloud’. Point clouds can be viewed in multi hue colours (based on signal intensity return) or true colour from a digital camera. This technique provides a solution for the rapid surveying of inaccessible surfaces or complex geometrical details. The data can be linked in 3D to your site grid and matched seamlessly with topographical survey plans, elevations and & sections.

The skill in observing and collating scan data comes from:
  • The ability to ‘register’ scan clouds together
  • Link them to the site survey grid to combine with conventional data
  • Get an even coverage of points at the required density
  • Manipulating the data to extract the specified deliverables.

Severn Partnership have developed a range of data processing workflows to enable rigorous solutions to point cloud registration and ensure a quality product.

We have a wealth of information on scanning spread over the site, so please explore or feel free to call or e-mail webenquiry@severnpartnership.co.uk for advice.

Links:

HDS scanning equipment

Sample Images & Visualisations

Uses of scan data

Benefits of laser scanning

Scanning Deliverables

Scanning software