GPS time (s)
Figure 2 3D coordinate difference between OTF and conventional method
GPS time (s)
Figure 3 Kinematic figuration closure from OTF
ambiguities can be added to double difference
carrier phase observations, then the 3D position
and velocity of the airborne GPS antenna can be
computed by using the sequential estimate
formula (4)~(11) or simply using least square
adjustment.
3 PRACTICE OF OTF AMBIGUITY
RESOLUTION
GPS photogrammetry practices were performed
in Beijing urban area in May 16, 21 and 22,
1996 respectivly. The photogrammetric area is
about 1500knr (50km*30km). The airborne
Wild RC20 camera was used to take
photographs with the focal length of 305mm and
the image scale of 1:8000 at the altitude of
2500m. Three Trimble 4000SSE receivers were
used to execute DGPS survey, one was onboard
the airplane and the other two were setup on
ground reference stations (BAS1 in airport,
BAS2 in the center of photogrammetric area).
The sampling rate of GPS receiver was 1 second.
Half hour static initialization was taken before
the airplane took off. GPS data for 17 flightstrips
in May 21 were processed using the above OTF
method Widelane observations were used in
data processing. Ratio threshold was set to 2 and
OVT threshold was set to 10 seconds. OTF
ambiguity resolution for each flightstrip was
very successful as shown in Table 2.
Three test procedures were used to test the
validity of OTF ambiguity resolution:
• To compare whether the ambiguities
resolved by OTF is the same as static
initialization.
• To compare whether the kinematic
baseline computed by OTF is the same as
conventional method
• To compute the kinematic figuration
closure from different reference stations.
7B-5-5