418 
Blake 
3.6 Laser scanning 
Laser scans were taken to infill the deck soffit not mapped by REDM or photogrammetry. The data-cloud was modelled and 
prepared for insertion into CAD by use of automated surface extraction software. The laser scan was unable to supply any edge 
definition of components generated to the required tolerance due to the complexity of model and this is characteristic of data-cloud 
derived data. The main value of the data was to add to patches of information on surfaces between the wire-frame edges and to 
determine surface profiles of the lower parts of the main ribs. The data received from the laser scan was generally of poorer utility 
than that produced by photogrammetry. 
Figure 4: Left: The data-cloud from the laser scan: 
Only surface interpolation is possible, the mapping of edges is 
not possible due to the low density of the data-cloud and the 
skewing of distance values caused by multiple signal re 
flection. 
Figure 4: Right: Automatic surface generation from the laser 
scan data-cloud. The mouldings of the castings have been 
corrupted beyond recognition. The generated surfaces are seen 
here exported into AutoCAD. (Laser scan by UK Robotic Ltd.) 
3.7 Measured 2D drawing 
2D details of the bridge’s joints were recorded by on-site plotting of measured detail directly onto 1:50 scale elevational plots. String 
levelled lines were used to assist this process. The pencil annotations were then inked in. Ironbridge Gorge Museum Trust 
Archaeology under the direction of Shelly White carried out this work. 
4. CONSTRUCTING THE SOLID MODEL FROM THE WIRE-FRAME CAD MODEL. 
Because the wire-frame from photogrammetry and REDM survey was built on a common control and CAD platform it could be used 
to form and fit solid components in true 3D positions. It was decided to use solid rather than surfaces modelling for the following 
reasons: 
• Edge extraction; a solid model will allow the extraction of line drawings without disruption by surface meshes. 
• File size is reduced compared to the surface model equivalent; 
• Component fitting and counterpart modelling is possible using Boolean operands; the fit between parts can be used to create the 
edges of components. 
• Element analysis is possible. 
Figure 5: Model under construction; the railing supports have been copied into positioned bounded by the wire-frame.