Use of Integrated Survey Techniques: Measuring the Iron Bridge 
417 
3.4 Reflectorless EDM (REDM) 
When access by scaffold was possible, REDM was used to in-fill gaps in the photogrammetric wire-frame. Stations were set up on 
the scaffold between each frame, and ties to the photogrammetric wire-frame were made by re-section to detail. By using instrument 
set-ups under the deck gaps could be in-filled at close range. All the REDM data was recorded in real-time into AutoCAD using 
TheoLt on a field computer, this process is manually operated 3D digitising. 
Figure 2: REDM set-up under the bridge deck 
tracing the crown bearer into AutoCAD in real 
time using TheoLt on a field computer. Right: 
The wire-frame completed by REDM. 
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The precision of the REDM work was adequate to model the deformation of the arcs for all five main ribs. The deck-plate edges 
were digitised in 3D and the distortion of the deck recorded. Compare to Figure 1: The Photogrammetric wire-frame. 
3.5 Isometric sketches and Narrative photography 
Isometric sketches were needed to adequately record and understand the fitting of jointing and engineering detail of hidden parts not 
visible in elevational drawing. Narrative close up photography was also taken of all joints and indexed by component 
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Figure 3: Sketches prepared on site during inspection for the completion of the wire frame data