\TA
ised in our experiments
'essungsamt Hamburg.
IR 87-20-828 acquired
otogrammetrie m.b.H,
the permission of the
coordinates extracted
em of the city of Ham-
> Hamburger Stadtent-
echts, Hamburg.
NTS
Ictive suggestions with
iim Rieger for suggest-
1 Schróder for support
ing valuable contribu-
ipt. For providing the
ler (Vermessungsamt),
Mr. Gleim (Stadtent-
d here have been done
the Al-Laboratory at
Iniversity of Hamburg,
Basedow and Tornow
igh-Precision Localiza-
mages. In Sagerer, G.,
ustererkennung 1995 —
many, 13.715. Septem-
I-601. Springer-Verlag,
| to Control Structures
riangulation in Digital
ogr. u. Fernerkundung
onfiguration Invariants
rmutation Transforma-
523-1532, 1994.
nz, 1993. Correspon-
P?-Invariant Represen-
and D.Forsyth, editors,
ter Vision, Ponta Del-
volume 825 of Lecture
—492. Springer-Verlag,
ing for Outer Orienta-
rame Controlpoints. In
on, D.C., 1992, volume
'es of Photogrammetry
. American Society for
, Bethesda, MD, 1992.
lles Verfahren zur au-
Luftbildern. Zeitschrift
115-122, May 1995.
Erkennung topographi-
uordnung. Zeitschrift
170-176, Nov. 1992.
1a 1996
GPS CONTROLLED STRIP TRIANGULATION USING GEOMETRIC
CONSTRAINTS OF MAN-MADE STRUCTURES
H. Ebadi and M. A. Chapman
Department of Geomatics Engineering
The University of Calgary
Calgary, AB, Canada, T2N 1N4
Tel: (403) 220-4981 Fax: (403) 284-1980
Email: hebadi @ensu.ucalgary.ca , mike @fuzzy.ensu.ucalgary.ca
WG 11/1
KEY WORDS: Photogrammetry, GPS, Adjustment, Bundle, Accuracy, Aerial Triangulation, Geometric Constraints, Reliability
ABSTRACT:
Conventional block adjustments (bundles or independent models) have been widely used to determine both photogrammetric point
coordinates and the exterior orientation parameters of photography for mapping purposes. Ground control points (planimetric points
along the perimeter of the block and relatively dense chains of vertical points across the block) are necessary to relate the image
coordinate system to the object space coordinate system and to ensure the geometric stability of the conventional block as well as to
control the error propagation. The major impact of cost and time consumption for ground control establishment on any mapping
project is the primary reason that photogrammetrists have been looking for a replacement for ground control by auxiliary data (e.g.
Global Positioning System). This paper describes a new technique for GPS controlled strip triangulation using geometric constraints
of man made structures (e.g., high voltage towers, high-rise buildings) located approximately along the flight line. The effects of the
different GPS measurement accuracies were also investigated. Both the precision and reliability analysis of the GPS bundle strip
adjustment with these constraints were carried out on simulated and real data.
1. INTRODUCTION
Since the launch of the Global Positioning System (GPS)
satellites in the early 80s, photogrammetrists have realized the
application of GPS for their particular interests (i.e., aerial
triangulation). With this technology, the position of the aircraft
at the individual exposure moments can be precisely
determined. These positions can then be introduced into the
combined GPS-Photogrammetric block adjustment as weighted
observations for the exposure stations reducing the number of
control points to a minimum. Aerial triangulation can even be
completed without any control points provided that the satellite
signals are not blocked during the flight mission (Lapine, 1992)
and as long as datum transformations are known.
However, there are a few problems that require attention in GPS
assisted aerial triangulation. These are the GPS antenna offset
calibration, interpolation of the exposure time, the initial phase
ambiguity resolution, signal interruptions, and datum problems
(Ackermann, 1992).
After kinematic processing of GPS observations, coordinates of
the antenna phase centres are available in the WGS84 reference
frame. Most ground coordinates are defined with respect to a
national coordinate system (e.g. UTM). The transformation
between these coordinate systems can be based on published
formulas (Colomina, 1993) or a set of common reference points
available in both systems. Elevations are usually related to the
ellipsoid and must be corrected for the geoid undulations.
Ground control points (planimetric points along the perimeter
of the block and relatively dense chains of vertical points across
the block) are mandatory for relating the image coordinate
system to the object coordinate system and to ensure the
geometric stability of the conventional block. The minimum
control requirement for absolute orientation is three non-
collinear points. For GPS-Photogrammetric block, this
condition is met by using GPS observations at the perspective
centres as control information. Since the GPS observations of
the exposure stations are almost collinear for strip triangulation,
the above condition is not satisfied and, therefore, the role angle
(i.e., around the flight direction) can not be recovered reliably.
This makes it necessary to use ground control points to solve
for the remaining exterior orientation parameters (Alobaida,
1993).
This paper reviews the concept of the GPS observable used in
the precise photogrammetric applications and describes a new
technique for GPS controlled strip triangulation using
geometric constraints of man-made structures (e.g. high voltage
towers and high-rise buildings) located approximately along the
flight line. The effects of the accuracies of different GPS
measurements were also investigated. A precision and
reliability analysis were performed on both simulated and real
data. All results were obtained using GAP (General Adjustment
Program) developed by the first author at the Department of
Geomatics Engineering (Digital Photogrammetry Group).
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B3. Vienna 1996
