Part B3. Istanbul 2004
jagery contained more
having connotations on
»nsequently, more tests
scales are required to
jx all scales. If so, the
hotogrammetry, having
ed in collected ground
ready exists or can be
the superlative solution
as issues affecting the
ause the two matched
ent terrain modelling
nmetry — each model is
tion of the same real-
ent structures, different
cies. Each of these
ach other but with the
neasurement techniques
anner. For example,
und height, as the detail
face at all times, while
n and surface objects.
n introduced. Although
hing of DEMs collected
ce change between the
|l of these effects mean
f height differences, it is
; compared; rather, it is
ves the solution open to
meters, resulting in an
ipparent from the output
jn error will appear to
differences; however,
ptimistic (Maas, 2000).
cies influencing the end
ers may contain error. In
d nature of the matching
ittainable, with the only
oice of initial parameter
. Multiple solutions may
significant problem is to
sition in space of the
onably large) parameter
n the final position of the
nge will mean that the
ved and, though height
tric position may suffer.
iimetric accuracy of an
entation occur, requiring
lues with airborne laser
to ensure true conjugate
spite this pessimism, the
ntations, with alternate
fully investigated, leaving
ximation of reality.
ONS
of photogrammetric DEM
to improve the efficiency
anual process. A surface
id used to minimise height
International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B3. Istanbul 2004
differences between a reference surface and a photogrammetric
DEM in a model coordinate system. To assess the effectiveness
of the procedure, a comparison was made between a
conventional orientation using GCPs and surface matching,
using digital SFAP models. DEMs were produced from
imagery captured from three flying heights. Following
extraction and orientation of the DEMs, a comparison with
checkpoints was made to determine the heighting precision of
each method. ^ These results showed that the matching
orientated improved the heighting precision of all three of the
DEMs, while the conventionally orientated surfaces suffered a
larger systematic error.
These results are encouraging, and have the potential to offer
photogrammetry a real benefit. In addition to the reduction of
systematic error, the surface matching algorithm offers an
increase in automation, the existence of additional verification
data in the form of the reference DEM, and increased
versatility, as data from many sources may be used. However,
further research may yet be carried out, to improve the
robustness of the algorithm and determine the effect of differing
solutions on the absolute position of the transformed DEMs. In
addition, the use of digital SFAP introduced significant errors
due to the scale and inherent instabilities of the image
configuration when compared with conventional large format
photography. Testing on more orthodox datasets would
therefore be of great value.
ACKNOWLEDGEMENTS
This work was carried out while the principal author was at the
University of Newcastle upon Tyne, and was supported by the
Engineering and Physical Sciences Research Council (EPSRC
grant GR/N23721/01) and the Royal Institution of Chartered
Surveyors (RICS Foundation). Thanks to the staff and students
of the University of Newcastle upon Tyne for assistance with
data collection.
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