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

27.03.2012 MCG 2012 - Stuttgart 3

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

27.03.2012 MCG 2012 - Stuttgart 4

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

27.03.2012 MCG 2012 - Stuttgart 5

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

27.03.2012 MCG 2012 - Stuttgart 6

antenna center

center of prism

axis

Configuration

Measurements

27.03.2012 MCG 2012 - Stuttgart 7

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

27.03.2012 MCG 2012 - Stuttgart 8

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

27.03.2012 MCG 2012 - Stuttgart 9

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

27.03.2012 MCG 2012 - Stuttgart 10

∑=

=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

27.03.2012 MCG 2012 - Stuttgart 11

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

27.03.2012 MCG 2012 - Stuttgart 12

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

27.03.2012 MCG 2012 - Stuttgart 13

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

27.03.2012 MCG 2012 - Stuttgart 14

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: annette.scheider@ingeo.uni-stuttgart.de alexander.beetz@ingeo.uni-stutgart.de volker.schwieger@ingeo.uni-stuttgart.de

27.03.2012 MCG 2012 - Stuttgart 15

Process

Evaluation

27.03.2012 MCG 2012 - Stuttgart 16

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