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Post-processed Kinematic Low-Cost GPS
Annette Scheider, Alexander Beetz, Volker Schwieger University of Stuttgart
Institute of Engineering Geodesy (IIGS)
Stuttgart, March 27th 2012
3rd International Conference on
Machine Control & Guidance
1) Equipment 2) Measurements 3) Evaluation 4) Conclusion
Structure
27.03.2012 MCG 2012 - Stuttgart 2
GPS receivers 1) Low-cost GPS receiver: AEK-4T from u-blox (receiving module LEA-4T)
• one frequency receiver (L1 signal) accuracy of positioning (code): 2.5 m CEP
• carrier signal can be stored by recording raw data on a computer 2) Geodetic GNSS receiver: GPS1200+ GNSS from Leica Geosystems
• Horizontal accuracy: (static mode)
(kinematic mode)
Comparable only for DGPS application, if short baselines are realized
Equipment
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0 1 2 3 4 50
2
4
6
8
10
12
baseline length in [km]ho
rizon
tal a
ccur
acy
in [m
m]
horizontal accuracy of Leica GPS1200 according to the baseline length
statickinematic
( ) ( )22 ppm 5.0mm 5 +
( ) ( )22 ppm 1mm 10 +
DGPS service: SAPOS (Satellite Positioning Service of the German Landesvermessung) • Offers a network of more than 270 reference station all over
Germany • Opportunity of creating virtual reference station near to the
measurement area
Equipment
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Processing mode
SAPOS service Horizontal accuracy
Real-time Real Time Positioning Service (EPS)
0.5 – 3 m
High Precision Real Time Positioning Service (HEPS)
1 – 2 cm
Post-processing
Geodetic Post processing Positioning Service (GPPS)
1 cm
Total station TCRP1201 from Leica Geosystems • Accuracy:
0.3 mgon (angular) (distance, tracking mode) • Use of a 360° prism Additional Hardware/Software: Panasonic Toughbooks Used Software: u-center, TEQC, LGO, wa1, LabView, Matlab
Equipment
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0 0.2 0.4 0.6 0.8 10
2
4
6
8
10
12
distance in [km]
horiz
onta
l acc
urac
y in
[mm
]
horizontal accuracy of Leica TCRP1201
statickinematic
( ) ( )22 ppm 2mm 5 +
Configuration • Measurement frequency of u-blox receiver: 1 Hz • Antenna center is placed directly over the center of prism • Construction of a shielding plate for the u-blox receiver
Measurements
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antenna center
center of prism
axis
Configuration
Measurements
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Prism and low-cost GPS receiver (with shielding plate), mounted on the measurement car
Prism and geodetic GPS receiver, mounted on the measurement car
Test scenarios Reference station for PDGPS applications: • Realized by a SAPOS reference station • Realized by a local reference station: u-blox receiver with shielding
plate Mounted Rover: 1) Low-cost GPS receiver and geodetic GNSS receiver 2) Low-cost GPS receiver: Without and with shielding plate 3) Initialization time: Different time intervals at the beginning
of the trajectories
Measurements
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Trajectories
• 3 days of measurements, several trajectories at each day • Reference points around the measuring areas Stationing of the total station, local reference station
Measurements
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380 400 420 440450
460
470
480
490
500
East [m]
Nor
th [m
]
straight line
380 400 420 440
450
460
470
480
490
500
East [m]
Nor
th [m
]
sinusoid
420 440 460
450
460
470
480
East [m]
Nor
th [m
]
U-turn
Parameters: Lateral and longitudinal deviation 1) Mean value of the 2) Scale factor
lateral deviation
sreference: distance between two points measured by total station sGPS: distance between two points measured by GPS sreference: calculated for a smoothed trajectory
Evaluation
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∑=
=n
iiq
nq
1
1GPS
reference
ssm =
Parameters: Problem: Single Measurements of the instruments are not synchronized!
Computation by comparing GPS points and interpolated points on the reference trajectory.
Evaluation
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205.3 205.4 205.5 205.6411.8
411.9
412
412.1
East [m]
Nor
th [m
]lateral deflections of Low-Cost GPS
referenceGPSlat. defl.
Evaluation
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Results Use of a shielding plate (Test scenario) Without shielding plate, there is an offset of more than 1 dm
between the reference trajectory and the trajectory measured by Low-cost GPS.
404 406 408 410 412
482
484
486
488
East [m]
Nor
th [m
]
trajectory without shielding plate
referenceGPS
72 74 76 78 80 82
918
920
922
924
926
East [m]N
orth
[m]
trajectory with shielding plate
referenceGPS
Evaluation
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Results
Reference Rover Configuration m VRS
u-blox with shielding plate, Initialization: > 60 min
3.5 0.9999697
u-blox with shielding plate, Initialization: 10 min
4.9 0.9999711
Leica Initialization: > 60 min 3.5 1.0000188 u-blox u-blox with shielding plate
Initialization: > 60 min 6.0 1.0000715
Leica Initialization: > 60 min 3.5 0.9999697
station total/σq
• Low-cost GPS (here u-blox LEA-4T) is applicable for kinematic position
determination in the post-processing mode • Shielding plate reduces systematic effects • Reference station: Reference service or local reference, For short baselines, a low-cost GPS receiver can be used as a reference station
• One-frequency-receiver reacts more sensitive to unfavorable measurement configurations
• Initialization time not necessary
Conclusion
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Thank you very much for your attention! Contact: Annette Scheider, Alexander Beetz, Volker Schwieger Institute of Engineering Geodesy Universität Stuttgart Geschwister-Scholl-Str. 24D 70174 Stuttgart Phone: +49-711-685 84057/-840427/-84040 Fax: +49-711-685 84044 E-Mail: [email protected] [email protected] [email protected]
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Process
Evaluation
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Total station Low-cost GPS
geodetic GPS
SAPOS
Raw data (*.ubx)
RINEX files RINEX files
Evaluated GPS trajectory data
Measurement data
Smoothed trajectory
comparison
Lateral deviation Longitudinal deviation