Chapman, David 
  
SHORT-BASELINE ACTIVE TRIANGULATION FOR CAD RECONSTRUCTION OF ROOM- 
SIZED INDUSTRIAL ENVIRONMENTS 
David Chapman’, Sabry El-Hakim 
"University College London, UK 
Department of Geomatic Engineering 
dchapman@ge.ucl.ac.uk 
“National Research Council of Canada, Canada 
Visual Information Technology Group 
Sabry.El-Hakim(@iit.nrc.ca 
Working Group V/3 
KEY WORDS: Active Triangulation, Range Imaging, As-Built Surveys 
ABSTRACT 
Recent developments in non-contact industrial range imaging systems have generally focussed either on very high- 
precision, short range, active triangulation systems capable of detailing measurement volumes of a few square metres or 
medium precision, time-of-flight systems with typical standoff distances of 2-50 metres. This paper will highlight a 
range of applications for medium precision (+/- 5mm) imaging of relatively complex, room-sized environments which 
are not currently well served by such systems. It will also suggest that the development of relatively short baseline 
active triangulation systems may lead to affordable, compact and robust short-range measurement systems capable of 
delivering range data suitable for such applications. A brief review of current systems for non-contact range-imaging 
will be followed by a detailed discussion of system trials undertaken with a modified Biris triangulation system in a 
typical engineering environment containing a wide variety industrial surfaces with a range of surface reflectivity 
characteristics. The authors will conclude that such a system may offer a compact and flexible alternative to competing 
technologies that could be readily deployed in complex small-scale industrial settings. 
1 BACKGROUND 
Many authors have documented an increasing demand for as-built modelling of large industrial facilities. Applications 
of such models range from very accurate surveys of tie-in locations to ensure first-time fit of new components to 
relatively crude volumetric models suitable for planning access or general facility management operations. One of the 
difficulties associated with such surveys is the development of appropriate specifications to ensure that measurements 
are captured at an appropriate density for the anticipated application. 
A number of measurement techniques have emerged to serve such markets. These include conventional geodetic 
surveying techniques based on total station intersection or radiation, close-range photogrammetry and, increasingly, the 
application of range-imaging sensors. 
Theodolite based surveys offer relatively high precision at the expense of comparatively slow data capture times. Since 
reduction of time spent on site is often of critical im: 
portance in such applications these methods are most commonly 
used for the accurate survey of a few tie-in points required for the fitting of new components and pipe-spools. 
Photogrammetric surveys can, in certain circumstances, offer comparable measurement precision and have the 
additional advantage that they enable very rapid data capture and potentially offer complete coverage of the facility for 
offline measurement. Unfortunately this offline measurement task remains a labour intensive operation that has been 
stubbornly resistant to attempts to automate image segmentation and object recognition in complex scenes. Against this 
background range imaging devices appear to have 
much to offer in that they enable the automatic derivation of dense 
clouds of 3D on the surfaces of the object. These point clouds offer the potential for some degree of automation of 
object extraction and thus raise the prospect of cheaper As-Built CAD modelling. Unfortunately many of the early 
range-imaging systems were often either very expensive, bulky or slow thus offering less flexibility than 
photogrammetric systems in the very cluttered environments typically encountered in many petrochemical and nuclear 
environments. 
  
  
122 International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B5. Amsterdam 2000. 
  
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