GPS for EWB Projects

1
GPS for EWB Projects

• Bryan Baker
• Vice President
• EWB Fort Collins Professionals
• Fall Technical Session 2008

2
(No Transcript)
3
Agenda

• How GPS Works
• Types of GPS
• Applications for GPS
• Obstacles for GPS

4
How does GPS Work?

• 24 Satellites (30 Currently)
• Orbit with a 55 rotation
• 20,200 km orbit
• 1 revolution in 11 hours 58 min

• High Orbit For
• Survivability
• Coverage
• Accuracy

5
GPS Signal Structure
Carrier L1 L2 Frequency 1575.42
MHz 1227.60 MHz Wavelength
19cm 24cm Code Modulation C/A-code L2C
(2005) P(Y)-code P(Y)-code NAVDATA N
AVDATA C/A - Coarse Acquisition Code P - Precise
Code (Y-Code when encrypted) NAVDATA - Satellite
health, satellite clock corrections, and
ephemeris parameters.
6
Trilateration
Distance D Speed of Light x Time of Signal
Flight
Autonomous Position /- 10 m (30 ft) error
(horizontal) /- 15 m (45 ft) error (vertical)
D
7
Code Differential Correction
Corrections can be applied Real-time Via Post
Processing
lt 1m
8
Carrier Phase Correction

• Carrier Wave
• L1 (19cm)

• Superimposed C/A Code

• Each chip is 293m long

Requires

• accurate antenna height
• clear view to the sky
• 5 satellites in view
• within 50km of base station
• synched measurements at base

9
Types of GPS

• Recreational Grade
• Autonomous
• Mapping Grade
• Code Differential
• Survey Grade
• Carrier Phase Differential

10
Recreational GPS
/- 10-15 Meter Accuracy
Applications Finding your car, fishing spot,
campsight, location on Google Earth, etc. Vehicle
Navigation Low accuracy, large scale maps.
11
Mapping GPS

• 2-5 Meters
• 1-2 Meters
• lt Meter
• lt30 CM (Foot)

Requires code differential correction from base
station and software to obtain specified
accuracies.
12
Surveying GPS

• lt1cm accuracy
• Requires Base station and rover receiver.
• Within 100km

13
EWB GPS ApplicationsRecreational Grade

• Supply mapping
• Journey / Trail Mapping
• Reference Point Location
• Google Earth Applications

14
EWB GPS ApplicationsMapping Grade

• Town / Village Maps
• GIS Data Collection
• Utility Mapping
• Hydrographic Mapping

15
EWB GPS ApplicationsSurvey Grade

• Topographic Mapping
• Property boundary location
• As-built for construction
• Construction layout