7B-5-1
OFF Method and Its Practice on Airborne GPS Data
Processing for Photogrammetry
Chen Xiaoming Liu Jiyu Li Deren
Wuhan Technical University of Surveying and Mapping
P. R. CHINA
KEY WORDS: GPS, OTF, Ambiguity, Kalman Filter
ABSTRACT
1 his paper proposes a new 01F (Ambiguity Resolution On the Flv) method based on double difference
Pseudorange/ carrier phase Kalman filter. With this method, the author has succeeded in processing the
airborne GPS kinematic data of the Beijing GPS aided photogrammetry project. Results show that this
method is capable of rapid and efficient resolving for carrier phase ambiguities for the case of long
distance as 50 km and height difference of 2400 meters. After complete fixing ambiguity, differential
positioning accuracy better than one decimeter can be obtained. In addition, this paper also executes
three evaluations for the reliability of OTF solution
1 INTRODUCTION
Ambiguity resolution On The Fly (OTF) is a
technique resolving integer ambiguity while the
receiver is in moving. Using OTF technique,
there is no need to perform static initialization,
which is necessary in conventional precise
kinematic positioning. Cycle slip, which is the
most troublesome problem in precise kinematic
positioning, is also easy to handle while using
OTF technique In case of cycle slip, integer
ambiguities can be resolved again on the fly.
Therefore, the flexibility and reliability of
kinematic positioning is improved.
In last decade, GPS kinematic positioning
technology has been used in photogrammetry
successfully. 3D photostation coordinates can be
determined at each exposure instant by
differential kinematic positioning which use one
airborne GPS receiver and one (or more) GPS
receiver set up on ground reference station to
receive GPS signals simultaneously. These data
are introduced as additional observations into a
combined block adjustment, resulting in densely
controlled blocks with highly uniform accuracy
distribution Introduction of these additional
observations allows for a significant reduction
for ground control required for photogrammetric
blocks and increases the efficiency of
photogrammetric mapping.
If using conventional kinematic positioning
technique in GPS photogrammetry, static
initialization is necessary before aircraft take off
This will not only extent observation time, but
also prolong the aircraft waiting time.
Additionally, a small swerve slope angle is
needed to avoid cycle slip and lost of lock. This
will cause a more fly distance and a longer time
interval between tlightstrips than that of
