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Figure 1b: Factors governing the measurement methodology 
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OP eon Requirements 
  
  
  
  
BACKGROUND 
The Department of Geomatics at The University of Melbourne 
was approached to assist in the measurement of the top section 
of a furnace material hopper shown in Figure 2. 
  
Figure 2. Diagram of the material hopper furnace top. 
The measurement was required to determine the amount of 
milling required to ensure that design specifications for a 
critical flange were met. The flange is initially over 
dimensioned so that it can be milled to the correct dimension 
once the component is completed. Milling of this flange is 
carried out just prior to installation by the manufacturer. It is 
critical that the furnace hopper meet the prescribed design 
specifications, as ultimately the flange must couple with 
existing components. Figure 3 shows an image of the furnace 
flange prior to milling 
OPERATIONAL CONSIDERATIONS 
A strict schedule was enforced to ensure that the component 
could be transported and placed into position according to the 
prescribed completion timetable. Restrictions for the project 
183 
dictated that milling data be supplied within a day of the 
component measurement. Once the initial milling was 
completed it was envisaged that the measurement would be 
repeated to recompute the flange thickness. The primary 
requirements in the project was the provision of coordinates to 
an accuracy of £0.5mm, the computation of spatial coordinates 
based on best-fit surfaces and of course rapid turn around time. 
A routine inspection of the site revealed very little of concern in 
terms of measurement obstructions. Despite the object size, 
relocation to a larger working area was possible through the use 
of an overhead gantry crane. However this was unnecessary as 
the object was located in a relatively uncluttered section of the 
workshop. The only obstructions were located on one side of 
the object where it was within one metre of an adjoining wall. 
A reasonable setback distance was available even with the 
appropriate consideration being given for workshop machinery 
and other components under construction. 
  
Figure 3. Image of the flange requiring milling 
Having inspected the site it was necessary to establish a 
measurement methodology capable of satisfying the accuracy 
and organisational requirements of the task. In order to 
compute the milling required it was necessary to first establish 
the as built state of the furnace hopper. From this data and the 
appropriate design dimensions it would be possible to relate the 
cutting data back to the surface of the flange. The project could 
be clearly segmented into two distinct components, namely 
coordinate determination and coordinate manipulation. 
To define the design coordinate system and the location of the 
flange, as well as provide checks on design dimensions, 
coordinate determinations was required for each of three key 
areas shown in Figure 4. 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B5. Vienna 1996