70°30’S 
1 
E 
70?31' 
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ouring 
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70°32 
n. Exposed 
ns of points 
ing errors in 
, which only 
ore than the 
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ularly in the 
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nfortunately, 
;ome of the 
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ed from the 
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| dimension, 
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he left-hand 
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al error is 
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he result is 
os a better 
rner is still 
attempts to 
strengthen control in the lower left corner but point 2004 is 
apparently poorly located, and the errors are unacceptable. 
The overall result of these tests was that the distribution of 
control in test 5 represented the best that could be 
achieved in this project. The results, while not comparable 
with the levels of accuracy to be obtained in temperate 
countries, are acceptable for mapping in this remote 
region. À further advantage is that the relative accuracy of 
measurements within the block is of the order of 1-2 m. 
The lower absolute accuracy is less important for practical 
use. 
RESULTS 
The output from the block adjustment was used with the 
AP190 analytical plotter to extract heights from one of the 
models of the block. Heights could only be reliably 
extracted on ridge-lines, on exposed rock and where 
crevasses or avalanche scars provided enough surface 
detail for stereo-matching on ice-covered surfaces. These 
elevations gave enough height control for the shape-from- 
shading algorithm described above to be used to extend 
contours onto the snowfields surrounding the central ridge. 
The map created (fig. 3), with contours at an interval of 
25 m, can be compared with an earlier map (fig. 4), 
compiled at a scale of 1:250,000, which was the most 
detailed line map of the area available prior to this work. 
ACKNOWLEDGEMENTS 
Dr. J. Sievers, Institut für Angewandte Geodäsie, Frankfurt, 
provided the georeferenced TM image. Mr. A. Perkins and 
Mrs J.W. Thomson, British Antarctic Survey, provided 
much helpful discussion. Dr R. Kirby and Dr C. Place, 
University of Edinburgh, were supervisors to RS during this 
project, which was undertaken as part of her MSc course. 
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Mcintyre, N.F., 1991, Mapping ice sheets with the 
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