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September 2015
PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING
to either the quality of the calibration process or the change
in the operational environment of the camera. Flying the
camera at 3,000 or 4,000 meters above ground exposes it to a
temperature that is extremely different from the temperature
of the laboratory during the calibration process. Such large
variations in temperatures and perhaps mechanical stresses
and vibration during aircraft take-off and landing may cause
some camera elements such as the lens, the CCD array or
the film to change their physical properties and dimensions,
resulting in systematic errors.
Today, additional parameters in the adjustment or so-called
self-calibration techniques can be added to the mathematical
model to reduce the effects of many of these imperfections
on the accuracy of the mapping products. Your observation
on the improved accuracy when using the self-calibration
option is correct as it can correct for many systematic
deformations. However you should practice caution as self-
calibration, especially the empirical model, sometimes results
in adverse consequences. It may weaken the solution due to
the added parameters to the solution. In addition, some of the
parameters modeled in self-calibration are highly correlated
and you should be careful in selecting them (for example,
the correlation between the principal point coordinate and
the some of the exterior orientation parameters). For the
empirical AP model and as a rule of thumb, the higher the
number of APs and order of the polynomial, the more tie/pass
points and perhaps more ground control points are needed for
safe modeling. Having ground check points is always the best
way to evaluate the stability of the solution and the resulting
“The well-known eight –parameter
model, which was originally developed
for film cameras decades ago, is found
to be equally effective to model physical
distortions in modern digital cameras.”
accuracy. It can tell you whether applying self-calibration or
any additional parameters is a good strategy for that certain
condition and camera. Applying GPS shift and drift modeling
and correction during block adjustment can also model many
of the systematic errors I mentioned earlier, which are not
related to the GPS. In other words, it may compensate for
not using the self-calibration option in the solution. Having
software that can handle self-calibration and other errors
modeling is always advantageous as it provides additional
tools to your arsenal as a photogrammetrist.
**Dr. Abdullah is Senior Geospatial Scientist and Associate at Woolp-
ert, Inc. He is the 2010 recipient of the ASPRS Photogrammetric (Fair-
child) Award.
The contents of this column reflect the views of the author,
who is responsible for the facts and accuracy of the data pre-
sented herein. The contents do not necessarily reflect the offi-
cial views or policies of the American Society for Photogram-
metry and Remote Sensing and/or Woolpert, Inc.
Part 1: Systems
Chpt 1: Energy & Matter (Robert Ryan,
Chpt 2: Sensors & Platforms (Charles Toth,
)
Chpt 3: New Technologies (Pierre LeRoux,
)
Chpt 4: UAS (Costas Armenakis,
)
Chpt 5: Cal/Val (Ayman Habib,
)
Part 2: Data Management
Chpt 6: Archiving, Storage, & Retrieval Systems (John Faundeen,
;
George Percivall,
)
Chpt 7: Image Processing & Analysis Methods (Marguerite Madden,
Sergio Bernardes,
Part 3: Applications
Chpt 8: Innovative Applications of RS (Bill Teng,
Bill Philpot,
Chpt 9: Information & Decision Support Systems (Stefan Falke,
;
Erin Robinson,
)
Chpt 10: Societal Bene ts (Rich Bernknopf,
; David Brookshire,
Chpt 11: Space Policy & Space Law (Joanne Gabrynowicz,
Karen Dacres,
Kevin O’Connell, kevin@innovative-
analytics.com; Kevin Pomfret,
Interested? Contribute
your knowledge,
expertise and material by
contacting chapter leads.
ASPRS Manual of Remote Sensing, 4th Edition
Editorial team:
Stan Morain, Editor-in-Chief
)
Mike Renslow, Co-editor
)
Amelia Budge, Co-editor
)
