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A combined block adjustment was made with all photos
(sidelap p=60%) and 8 control points (2 in every block
corner - see figure 5) and also with a reduced set of 70
photos with a sidelap of 20%.
omis [p=60% |= iin
16 =
Figure 8: results of the bundle block adjustment
A: without GPS
B: combined adjustment old method
C: combined adjustment new approach
Figure 8 shows the results of the bundle block
adjustments of the block Oesingen with the program
system BLUH at independent check points. On the left
hand side are the results of the adjustment with all 140
photos and a sidelap of 6096. The stable block
configuration do not show an advantage of the new
method of combined block adjustment, the results of the
traditional method is in X and Y with x 3.5cm nearly the
same like with the new method of +3.6cm. In the height
the old method shows +8.1cm and the new method
+9.5cm.
The results of the block adjustment with only 70 photos
and a sidelap of 20% can be seen on the right hand side.
The horizontal accuracy is approximately the same for
both methods, but this has been expected in advance - in
general in the block adjustment the horizontal geometry
is stable also without GPS and without additional vertical
control points. The vertical component is different. À
block with just 20% sidelap and no crossing flight strips
is not stable in the height. Also the traditional method of
combined block adjustment will not solve the problem
because every flight strip is shifted individually, but here
the advantage of the new approach can be seen - with
the old method a vertical accuracy of only SZ=+16.5cm
is reached, by the new method the vertical component is
improved to SZ=+10.8cm.
Beside the general additional parameters for the self
calibration one unknown for every satellite has been
introduced. In addition unknowns for the datum shift (3
components) and for the determination of errors of the
antenna offset are required. If all used strips have been
flown in the same direction, it is not possible to indroduce
unknowns for the datum shift and for the antenna offset.
6. BENEFITS FROM THE NEW APPROACH
The general approach of shift and drift parameters uses
independent GPS positions for each strip. The new
approach using satellite geometry considers also the
geometric relationship between strips. It is possible to
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B3. Vienna 1996
estimate one set of additional parameters for the
complete block obeying strictly the functional GPS
model. Additionally, no special investigations on satellite
geometry changes during a strip are required for the GPS
processing.
An additional problem is the distance dependence of
precise GPS. Over large distances the block adjustment
can constrain the ambiguity resolution. Detailed
investigations on this topic are necessary.
The number of additional parameters is generally
reduced, if not during every curve flight all satellite
signals are lost.
7. CONCLUSION
For a number of applications in photogrammetry, which
primarily depend on the scale, only GPS positions
accurate to some decimeter or less are sufficient. For
high precise demands, the correct ambiguity resolution is
required to compute GPS positions at the 5 cm level.
A new approach of combined block adjustment has been
presented, which uses strictly the functional GPS model
to estimate remaining systematic errors in the GPS
positions caused by false ambiguity resolution.
Even the re-substitution of the improved ambiguity terms
is feasible, however, it is not of much interest as the GPS
processing techniques improve.
The first test of a block with a limited size always shows
the advantage of the new method. Crossing flight strips
can be avoided even in blocks with just 4 control points
and 209^ sidelap.
REFERENCES
Jacobsen, K., 1993. Experiences in GPS Photo-
grammetry, PE&RS, Vol. 59, No. 11, pp1651-1658.
Jacobsen, K., Block Adjustment with Precise Differential
GPS-Data. ISPRS Commission lll, Working Group 1,
Munich 1994
Jacobsen, K, 1996. Operational Use of Combined
Bundle Block Adjustment with GPS-Data of the
Projection Centers Combined, ASPRS/ACSM Annual
Convention, 1996, Baltimore
OEEPE, 1994. Empirical Results of GPS-Supported
Block Triangulation. European Organization for
Experimental Photogrammetric Research, Official
Publication, No. 29.
Schmitz, M., 1995. Integrated GPS-Aerial Triangulation
Orientation. Presented at the Workshop Integrated
Sensor Orientation, 1995, Barcelona, Spain.
Seeber, G., 1993. Satellite Geodesy. Foundations,
Methods, and Applications. Walter de Gruyter, Berlin,
New York.
Seeber, G., V. Bóder, H.-J. Goldan, M. Schmitz, G.
Wübbena, 1995. Precise DGPS Positioning in Marine
and Airborne Applications. IAG Symposium G1, IUGG
General Assembly, July 1995, Boulder, USA.
The cooperative research of the Institut fur Erdmessung
(IE) and the Institut fur Photogrammetrie und
Ingenieurvermessung (IPI) is supported by the Deutsche
Forschungsgemeinschaft (DFG).
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