3rd International Conference on

Machine Control & Guidance

Post-processed Kinematic Low-Cost GPS

Annette Scheider, Alexander Beetz, Volker Schwieger University of Stuttgart Institute of Engineering Geodesy (IIGS) Stuttgart, March 27th 2012

Structure

1) 2) 3) 4)

Equipment Measurements Evaluation Conclusion

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Equipment 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: (5 mm)2 + (0.5 ppm )2 (static mode)

(10 mm)2 + (1 ppm )2 (kinematic mode)  Comparable only for DGPS application, if short baselines are realized MCG 2012 - Stuttgart

horizontal accuracy of Leica GPS1200 according to the baseline length 12

horizontal accuracy in [mm]

•

10 8 6 4 static kinematic

2 0

0

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4 3 2 1 baseline length in [km]

5

3

Equipment 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 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

Geodetic Post processing Positioning Service (GPPS)

1 cm

Postprocessing MCG 2012 - Stuttgart

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Equipment

• Use of a 360° prism

horizontal accuracy of Leica TCRP1201 12

horizontal accuracy in [mm]

Total station TCRP1201 from Leica Geosystems • Accuracy: 0.3 mgon (angular) tracking mode) (5 mm)2 + (2 ppm(distance, )2

10 8 6 4 static kinematic

2 0

0

0.2

0.4 0.6 distance in [km]

0.8

1

Additional Hardware/Software: Panasonic Toughbooks Used Software: u-center, TEQC, LGO, wa1, LabView, Matlab

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Measurements 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 axis

antenna center

center of prism

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Measurements Configuration

Prism and low-cost GPS receiver (with shielding plate), mounted on the measurement car MCG 2012 - Stuttgart

Prism and geodetic GPS receiver, mounted on the measurement car 27.03.2012

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Measurements 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

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Measurements Trajectories sinusoid 500

490

490

480 470

470 460

450

450 400

420 East [m]

440

480

480

460

380

U-turn

North [m]

500

North [m]

North [m]

straight line

380

470 460 450

400

420 East [m]

420

440

440 East [m]

460

• 3 days of measurements, several trajectories at each day • Reference points around the measuring areas  Stationing of the total station, local reference station

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Evaluation Parameters:  Lateral and longitudinal deviation 1) Mean value of the 2) Scale factor lateral deviation 1 n q = ∑ qi n i =1

sreference: sGPS:

m=

sreference sGPS

distance between two points measured by total station distance between two points measured by GPS

 sreference: calculated for a smoothed trajectory

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Evaluation Parameters: Problem: Single Measurements of the instruments are not synchronized! lateral deflections of Low-Cost GPS

North [m]

412.1

412

411.9

reference GPS lat. defl.

411.8 205.3

205.4 205.5 East [m]

205.6

Computation by comparing GPS points and interpolated points on the reference trajectory. MCG 2012 - Stuttgart

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Evaluation Results Use of a shielding plate (Test scenario) trajectory with shielding plate

trajectory without shielding plate

926

488

North [m]

North [m]

924 486 484 reference GPS

482 404

406 408 East [m]

922 920 reference GPS

918 410

412

72

74

76 78 East [m]

80

82

 Without shielding plate, there is an offset of more than 1 dm between the reference trajectory and the trajectory measured by Low-cost GPS.

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Evaluation Results Reference VRS

u-blox

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Rover u-blox

Configuration with shielding plate, Initialization: > 60 min

u-blox

q / σ total station

3.5

m 0.9999697

with shielding plate, Initialization: 10 min

4.9

0.9999711

Leica

Initialization: > 60 min

3.5

1.0000188

u-blox

with shielding plate Initialization: > 60 min

6.0

1.0000715

Leica

Initialization: > 60 min

3.5

0.9999697

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Conclusion • 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

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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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Evaluation Process Total station

Measurement data

Low-cost GPS

geodetic GPS

SAPOS

Raw data (*.ubx) RINEX files

Smoothed trajectory

RINEX files Evaluated GPS trajectory data

comparison

Lateral deviation MCG 2012 - Stuttgart

Longitudinal deviation 27.03.2012

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