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currently underway under a European Community funded 
research programme. 
Results from the trials, presented in section three, 
demonstrate the utility of this method and lead to the 
conclusion that digital photogrammetry may play a 
_ major role in the creation and maintenance of accurate 
as-built plant records. 
Measurement techniques for CAD modelling 
Theodolite intersection has been widely used during 
construction to verify design plans and to provide 
control for close range photogrammetry (Legac, 1991) 
however with the progressive reduction in permissible 
radiation exposure for human operators and the relatively 
long data acquisition times it is clear that manual 
systems such as ECDS are unlikely to be deployed in 
active areas. 
Whilst the development of automated theodolite 
intersection systems (e.g. Leica SPACE system; Kyle, 
1990) may allow remote operation the emphasis of 
these systems on high precision pointwise 
measurement of objects for on-line intersection is not 
appropriate if rapid acquisition is dictated by the 
environment. Thus whilst the system described in the 
body of this paper has much in common with such 
techniques the emphasis is on rapid acquisition of data 
with off line CAD restitution. 
Obviously close range photogrammetry offers the 
capability for rapid data acquisition and has thus been 
widely utilised in radio-active areas (Clayton, 1989; 
Legac opp.cit.; Martin, 1988 etc.). In the case of 
conventional photo-chemical imaging the limiting 
factor in successful use of such techniques is the 
fogging of the film by the radiation (See Figure 2). 
  
1.00 
0.90 
0.80 ; 
0.70 n 
0.60 24 
Fogging 0.50 x 
0.40 
0.30 
0.20 
0.10 
0.00 4 + 
0.00 0.13 0.50 2.00 8.00 32.00 128.0 512.0 
  
     
  
—7 25.00 ASA 
— 50.00 
-- 100.00 
  
  
  
Integrated Dose (R) 
  
  
Figure 2. Radiation fogging of photographic film 
  
An empirical formula developed by Clayton and Jones at 
the UK Central Electricity Generating Board (now 
Nuclear Electric) presents a relationship between the 
fogging of panchromatic film and absorbed dose of 
Gamma activity around 1.0 MeV such that 
  
* The project is one of 16 funded under the European 
Community TELEMAN programme which is directed 
towards the development of tools for 'Remote operations in 
hazardous or disordered nuclear environments’. 
Fare LT 10 (ASAP R 
where F = fog level = (t-t tert) 
t=transmittance of exposed film 
t =transmittance of unfogged film 
o 
t=transmittance of fully fogged film 
ASA=fiim speed ASA number 
R = absorbed radiation dose in Rads. 
In most circumstances fogging will occur at integrated 
doses which are higher than the acceptable level for 
human operators. Thus the availability of systems for 
the deployment of the cameras may limit the utility of 
photographic acquisition. However, with sufficient 
ingenuity, photogrammetric measurement is possible in 
even highly active areas by minimising exposure to the 
radioactive field through sophisticated remote handling 
methods (Clayton, 1989 ). Restitution of photographic 
images may be accommodated on existing analytical 
plotters which link to 3D CAD modelling packages 
(e.g. the Leica DSR range which may be used with 
Intergraph's MicroStation CAD tool ). Alternative 
strategies include the digitisation of photography on a 
high precision scanner with restitution and CAD 
construction on a softcopy photogrammetric 
workstation. Such a system has been implemented in 
the UK by Offset Services Ltd and offers the advantage 
that photogrammetric tools can be closely coupled to a 
range of plant modelling packages. Many other softcopy 
workstations are either commercially available or at an 
advanced stage of development (see Ebner et.al., 1991 
for a recent summary ). The use of such tools seems to 
offer considerable flexibility in the construction of CAD 
models - a theme which is developed more fully in 
Section 2. 
Measurements from holography have found application 
in a number of diverse fields including aerospace, 
electronics and even medical and dental applications. 
Holographic recording has been shown to be effective in 
highly hostile environments (to 10° Rads, Glanville et 
al, 1985). Holographic techniques offer advantages over 
conventional close range photogrammetry in that they 
provide very dense storage of information (Tozer and 
Webster, 1980) and, since no image forming optics are 
employed, problems relating to depth of field may be 
bypassed. Most importantly the data stored provides 3D 
information about the scene rather than the 2D 
information stored in conventional intensity images. 
Thus a single holographic record has the capability of 
covering a three-dimensional field that would need 
perhaps multiple stereo pairs of images for three 
dimensional reconstruction by close range 
photogrammetry (Gates, 1986). This makes holography 
a very attractive proposition in the densely cluttered 
environments typical of nuclear installations where 
accessing suitable vantage points is often very difficult. 
However when large objects, such as engineering 
structures, are to be recorded the stability of the imaging 
system may give rise to some difficulties. Holographic 
recording media are relatively slow (rated at a fraction of 
  
   
   
  
  
   
   
  
   
   
    
  
  
    
   
   
   
  
   
    
  
    
   
    
  
   
   
   
   
  
   
   
   
  
   
   
   
   
  
  
   
  
  
  
  
   
  
  
  
  
  
   
   
  
  
    
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