cranes had to be analyzed structurally to ensure that they 
had adequate lifting capacity. 3-dimensional CAD models 
were required which would be suitable for further 
manipulation and interrogation by the clients CAD 
system. 
  
  
  
  
  
  
  
  
Fig. 8 & 9 Detail of wire frame and hidden line views 
  
The photography required for each gantry crane was taken 
from a variety of platforms, an elevated hoist, the floor 
and even on the cranes themselves. The cameras used 
were a Wild P-32 and a Hasselblad SWC fitted with a 
reseau plate. The machine halls where the gantry cranes 
operated provided a challenging environment for 
analytical photogrammetric methods. They were dimly lit 
and echoed continuously with the noise and vibration of 
turbines and generators. Additional illumination from 
portable spot lamps was essential but even so the 
recommended exposure times were slow. With the 
exacerbating effect of reciprocity these were commonly 
in excess of 45 seconds. The vibration within the halls 
caused blurring on some images. Particularly affected 
were those acquired from the elevated hoist when fully 
extended. The films were processed at the end of each day 
to ensure coverage and to provide the opportunity of 
retaking any photography. Fortunately this was not 
  
   
required. The ground control survey was also affected by 
vibration and many additional survey measurements were 
taken in order to derive a reliable 'mean' set of 
measurements. The physical restrictions of the machine 
halls prevented all survey and photography being obtained 
with the gantry crane in the same position. One half of the 
crane was photographed and then the crane had to be 
moved to enable coverage to be obtained from the other 
side. This movement also caused a problem in the 
definition of the survey datum. This was resolved by 
assigning fixed coordinates to two target points on the 
gantry crane itself. This resulted in a survey network in 
which the gantry was static, and the tacheometric stations 
appeared to have moved relative to each other. There were 
approximately ten photogrammetric models for each 
gantry crane. These were established on the IMA. 
Corrections were applied to the Hasselblad photography 
to compensate for film unflatness and lens distortion 
(Robson, 1990). 
Initially, the major structural planes were digitised 
separately. These planes corresponding broadly with the 
top, bottom and sides of the gantry crane. This division 
may appear arbitrary but this approach is essential when 
delineating complex objects into a 3-dimensional CAD 
system. If every possible feature is digitised using any 
single photogrammetric model confusion will arise which 
may introduce errors during subsequent editing and also 
increase editing time itself. The 3-dimensional model of 
complex objects such as the gantry crane would be 
difficult to interrogate and use effectively if represented 
solely by line strings. By editing these line strings into 3- 
dimensional geometric shapes to represent beams, metal 
plates and ’L’ shaped supports, individual components 
which actually comprise the object are identified and 
reveal details of construction that are essential to the 
engineer. The finished models were then field completed 
by the client, to check the accuracy of the model and to 
add any important detail features. These included the 
gantry rails, and small mechanical parts of the cranes that 
were not visible on the photography. 
Chemical Plant 
Plant design engineers have had available to them for 
some time 3-dimensional piping design CAD packages. 
However, whilst the new areas of plants undergoing 
refurbishment or expansion have had the advantage of 
being designed 3-dimensionally within a CAD system, 
existing plant constructions are traditionally stored in a 
2-dimensional form on paper or film drawings and 
consequently have had a limited use in the new design 
(Bracewell & Klement, 1983). 
EPU were asked to produce a 3-dimensional model of part 
of a chemical plant for ventilation studies and safety 
certification. There were existing plans of the area, but 
because of the time it would have taken to convert these 
into a 3-dimensional model it was decided to undertake a 
photogrammetric survey of the site. This had the 
advantage not only of speed but also it would provide an 
“as built’ model rather than an 'as designed’ one. The area 
of interest covered approximately 100 metres by 100 
metres. This ruled out the use of vertical aerial 
photography on economic grounds. 
The 3-dimensional nature of this site meant that photo 
control had to be carefully selected so that it was not only 
visible on one elevation of the area, but also on