Accuracy We) 
Method X RMSE Y RMSE Z RMSE i 
Metres Pixels Metres Pixels Metres Pixels 
Stereo 0.10 0.6 0.09 0.6 0.25 16 — 
Ortho 0.17 1.1 0.11 0.7 1.30 9,4. à 
Repeatability (Precision) A 
Method X RMSE Y RMSE Z RMSE 
Metres Pixels Metres Pixels Metres Pixels 
Stereo 0.05 0.3 0.04 0.3 0.14 0.9 
Ortho 0.04 0.3 0.05 0.3 0.06 0.4 
  
  
  
  
  
  
Table 4: Accuracy and repeatability statistics for the Raskelf survey (comparison against ground survey). 
5. DISCUSSION 
This paper has presented the results of two aerial 
surveys using a high resolution digital camera and low 
cost photogrammetric processing software. In the first 
survey, a method of map revision and intensification has 
been outlined utilising low cost photogrammetric and 
GPS techniques. Initial results have indicated that the 
accuracy of each of the methods used in the process are 
comparable, and the overall technique suitable for the 
verification and revision of existing datasets. Imagery at 
this scale is not, however, suited to large scale mapping 
from scratch due to its poor ground resolution. 
Results from the second survey have illustrated the 
potential of the camera to produce large scale mapping 
comparable to the largest dataset in the United Kingdom. 
More care in the mapping and editing process should 
ensure that the mapping is within the OS specification. 
Unfortunately the small format of the camera means that 
many images are required to map an area of any 
substantial size and this is labour intensive, both in terms 
of controlling and processing the imagery. 
Both surveys used instruments to control the 
'photography' that would already be in place in a civil 
engineering workplace. Further, results have indicated 
that monoplotting from orthophotos (a technique 
especially useful for non-photogrammetrists) yields a 
similar planimetric accuracy (the main requirement for 
mapping data) to stereoplotting. The automated low cost 
production of DEMs (King et al, 1995) is a further 
incentive for such technology to be implemented 
alongside surveying tools currently utilised by engineers. 
6. CONCLUSIONS 
Although, at present, the drawbacks associated with the 
techniques outlined in this paper mean that it is unlikely 
to find favour for commercial use in mapping, the 
potential of ‘still video’ technology in this area has been 
shown. Improvements in the size, resolution and capture 
rate of CCD ‘still video’ cameras will mean that the kind 
of accuracies achieved in the Raskelf survey will soon be 
possible for much larger areas using commercially 
accepted aircraft. The lack of an aerial digital camera is 
the last major stumbling block in the world-wide 
acceptance of digital photogrammetry. The rapid 
advancement of products being produced, both by 
photographic and electronic multi-nationals, must mean 
that such a camera cannot be far away. 
Acknowledgements 
The author would like to thank the EPSRC for funding 
this research; Dr. Ron Graham for his enthusiasm and 
invaluable help with the photography and Tommy Jordan 
of R-Wel Inc. for his technical help with the DMS. 
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