Framegrabber 
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T NS | = | off-line analysis 
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EH EN Pan/tilt unit, mounted 
    
on remote controlled 
vehicle. 
    
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Figure 4. Principal components of the Hazmap system 
  
(Quartly, 1988), their failure is gradual rather than 
catastrophic. 
Whilst both CCD and vidicon imagery have been used 
for photogrammetric modelling they each suffer from 
some limitations. In both cases the imagery is generally 
of very limited resolution. Most systems rely upon 
either measurement of the analogue imagery, by 
digitisation of the analogue CCTV video standard signal 
by a frame grabber (each typically yields an image of 
512 by 512 pixels) or by direct interrogation of the 
CCD chip. 
In the case of vidicon cameras photogrammetric 
measurement is also inhibited by geometric instability 
caused by the electro-magnetic fields encountered within 
active plant cells, these effects can be mitigated, to 
some degree, by the adoption of reseau plates. 
The HAZMAP project uses CCD cameras because of 
‘their low cost, small size and radiation tolerance (to 10° 
R) which combine to make them suitable for the 
proposed prototype. Furthermore, small format digital 
cameras with higher radiation tolerance (to 10° R) are 
being developed within the TELEMAN programme and 
should be available if the situation demands. 
CCD cameras offer the geometric stability demanded by 
photogrammetric operations but are still constrained to a 
limited format. Whilst cameras with 2000 by 2000 
pixel resolution are increasingly available (Luhmann, 
1990) the HAZMAP remote measurement system was 
designed around standard CCIR cameras (digitised to 768 
x 575 format) mounted in an instrumented pan/tilt unit 
to enable the construction of a mosaic of individual 
image tiles. This results in a hybrid imaging system 
with a virtual field of view of 400 gons by 120 gons 
(Figure 4). This approach is similar to that outlined by 
Wester-Ebbinghaus (Wester-Ebbinghaus, 1988a) 
although the approach to modelling the system is rather 
different. The design of this system was predicated by 
the knowledge of radiation tolerant components being 
developed within the TELEMAN programme. The 
remote measurement unit will be mounted upon either a 
tracked vehicle or a long reach arm for system trials. 
Results to date are based upon deployment of the unit 
on stable tripods during image acquisition. 
The photogrammetric module. 
This module comprises: 
an image management database; 
image measurement tools; and 
» orientation and transformation toolbox. 
The image management database enables combines the 
image tiles with camera parameters which define the 
geometry of the hybrid imaging system. Camera 
calibration information which relates the geometry of 
the CCD chip to the rotation centre of the pan/tilt unit 
is derived by the method suggested by Huang & Harley 
(Huang & Harley, 1990). Angular information which