GENERIC LASER SCAN REPORT

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1. Rapid Laser Scanning

The laser scanner is a tripod mounted device that measures all visible detail from its central position. Using a high intensity setting, each bubble contains up to 101,000,000 individually measured pixels, each with an x,y,z co-ordinate and an intensity which is dependant on the reflectivity of the object observed. A higher pixel intensity is possible, but the high setting is the best compromise between time/archive size versus observed detail definition. The scanner does not need illumination to operate and can measure detail up to a distance of 80m, but definition intensity decreases over distance. The accuracy of the detail varies, depending on the reflectivity of the object observed, but is rated at +/-5mm in most conditions.

The scanner is set up in a location to best “see” local detail. It is re-positioned for each scan. The proximity of the scans depends on the amount of detail and congestion in the survey area, and the available locations where a tripod set up is possible. Each scan takes a minimum of 7 minutes to complete, once the instrument is set up.

Data directly below the scanner is not captured in that scan. These blind spots can be expressed as a cone 50 degrees directly down. Adjacent scan positions will cover these shadows and other blind spots

Targets, with known co-ordinates are located about the scanner to allow the scan software to resect the scanner position using a seven parameter least squares transformation. This identifies the co-ordinate and orientation of the scan. The co-ordination of the targets is described below.

Targets types are varied but there should be enough semi-permanent positions to allow follow-on laser scan projects to be orientated easily.

2. Control

Scanner targets are observed using a prism and total station, which observes vertical and horizontal angles, and distances, thereby enabling a 3D co-ordinate of the observed point relative to the instrument, to be recorded.

With careful observation, accuracies of 1mm and less are achievable, in a local grid.

Observations will be taken to existing control, where it exists, to enable a transformation into the local co-ordinate system.

Alternatively, observations may be taken to existing structures to establish a platform grid which will be used on future visits.

3. Registration of Scans

Each scan is converted from an uncompressed format (.zfs) to a compressed format (.zfc). A minimum of 4 targets are identified in each scan , which allows the software to transform each scan into the Control Network. This is computed as a least squares transformation and calculates a position and orientation for the scanner.

These scans are processed further to generate a Point Cloud (.lfd format), where all scans for an area may be viewed at once when used with “LFM Server” software.

A “Truview” dataset can be generated from the same scan data. This allows all scans to be viewed as a “bubble view” in the Windows Explorer program. No licensing is required to view in this format.