International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B4. Istanbul 2004
It should be emphasised that naive does not mean non-
optimised, as the existing routines had been compared with
a number of other implementations and had been found to
be superior.
Table 6: Timings (Pentium IV 1.7GHz, 58 Photos, 1207
Redundancy)
Solution Solution Implementation
Technique Naive 'C' | BLAS/LAPACK
Cholesky
decomposition 92.3s 10.9s
Reduced
normals 33 3s 5.2s
6 CONCLUSIONS AND OUTLOOK
Difficulties with the data used during testing mean that it is
not possible to state any conclusions definitively. However,
the results appear to indicate the following:
+ Directly including GPS pseudoranges in a photogram-
metric bundle adjustment yields relative mapping ac-
curacies close to those available from a network con-
trolled using ground control points.
» Despite using exactly the same data, directly includ-
ing GPS pseudoranges in a photogrammetric bundle
adjustment provides better results than when single-
point exposure station position observations are used.
» Regardless of whether the pseudoranges are directly
included in the adjustment or single-point exposure
station position observations are used, precise orbits
and clocks can substantially improve mapping accu-
racy.
With regards to the software implementation of the com-
bined GPS/photogrammetric adjustment, an object-orient-
ed program design can improve both maintainability and
extensibility of the software. Also, use of tuned linear al-
gebra libraries can dramatically improve performance of
numerically intensive adjustment computations. Their use
is advised even for moderately sized adjustment problems.
To the best of the author’s knowledge, neither the tech-
nique of including the GPS pseudoranges in a bundle ad-
justment, nor a hierarchical combined photogrammetric/
GPS/network adjustment have been discussed in the litera-
ture before. Both are, however, straightforward extensions
of existing practices.
A number of investigations closely related to this paper
have been performed but could not be included here be-
cause of length restrictions. Foremost among these are
tests with fewer than three satellites. Also, the technique
of including raw GPS measurements has been extended to
include double-difference code ranges. Both of these in-
vestigations will be discussed in a forthcoming paper.
Finally, it should be noted that the ultimate goal of this re-
search is the creation of an integrated GPS/photogrammet-
ric processing package. In such an arrangement, the photo-
grammetric adjustment would feed position updates into
a GPS Kalman filter, aiding the GPS ambiguity resolution.
The GPS filter would, in turn, feed highly accurate ambigu-
ity resolved carrier-phase ranges into the photogrammetric
adjustment.
ACKNOWLEDGEMENTS
As the author's supervisor, Dr. Naser El-Sheimy is thanked
for his ongoing personal and financial support. Joe Hutton
and Dr. Mohammed Mostafa at Applanix, Inc. are thanked
for providing the data used in this study. Funding for this
research was provided by the Killam Trusts and the Natu-
ral Sciences and Engineering Research Council of Canada
(NSERC).
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