- 95 - 
Fig. 1 Masking produces shadow effect 
2. 3D Data Collection and Imaging Systems for 
Documentation 
The various systems used in the Thealasermetry trials are out 
lined below: 
Prior to embarking on the testing in pilot sites, a decision also 
had to be taken with regard to the type of digital camera to be 
employed. The MCR’s 2D Imaging Department had been in 
existence since 1999 and was originally equipped with at least 
one eye firmly fixed on the option of going completely digital. 
It had at its disposal anything from a Nikon Coolpix 950 to a 
Nikon D1 to a Hasselblad 550 equipped with a Megavision SI 
back. Constant experimentation with digital photography, in 
cluding over 4000 images shot with a SONY Cybershot DSC- 
70, appeared to prima facie confirm the findings of Beraldin et 
al when they reported that the use of a low-cost Digital Camera 
was satisfactory 5 Thus, although MCR was due to procure at 
least two other digital backs ranging from 96 Mb file size with 
4,000 x 4,000 resolution (medium format) to 549 MB file size 
with up to 12,000 x 15,990 resolution (large format), it was not 
deemed necessary to await the availability of such equipment 
for the tests on the Thealasermetry hypothesis. The resolution 
possible from any one of the smaller format digital cameras 
available appeared to be more than sufficient for the outline 
rendition required to test metric accuracy. 
In close range photogrammetry, 6 digital cameras can offer the 
precision of analogue cameras, and today it is claimed that the 
5 BERALDIN, GU1DI op.cit at pages 1 and 2 
6 Photogrammetry allows the user to produce very accurate outlines 
in 3 dimensional polygons. Lines and points can also be ‘traced’ 
with a cursor across the surface of the model derived from the 
latest generation backs for large format cameras can provide 
even more detail in the same shot for the same area than a con 
ventional 5x4 inch film. 7 * In our experiment we compensated 
for the fact that we used a 35mm size camera and not a medium 
or large format by shooting more digital stereopairs, and adding 
more control points. This is a satisfactory approach for the 
integration exercise envisaged in stages 2 and 6 outlined above 
but would possibly increase propagation error when completing 
stage 8. 
In our sample photogrammetric survey we opted for a Nikon D1 
digital camera. The features of this camera include: 
• 2.74 mega pixel digital 
• (24mm x 16mm format back) 
• with a 24mm lens camera 
• Manual Exposure Control 
This camera offers the possibility of shooting restricted areas 
with little stand-off distance. In comprehensive survey projects 
however, it is planned to later mostly use (where distance per 
mits) a digital back for a 5 x 4 inch camera capable of produc 
ing up to 549 megabit files of data per shot. 
For the control of the orientation and integration of the extra 
stereo models required when carrying out data acquisition with 
the Nikon Dl, the Theodolite Total Station surveyed photo 
control becomes more important. 
MCR’s strategy for 3D laser imaging finally settled on procur 
ing a minimum of 4 different systems: 
7 
stereopairs. As the line drawing is made by the operator, tracing 
complex surfaces, such as eroded stone, can be a long process 
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