gnss 101 “bringing it down to earth” 101 “bringing it down to earth” ... the space segment...
TRANSCRIPT
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GNSS 101“Bringing It Down To Earth”
Steve Richter – Frontier Precision, Inc.
NGVD 29
Datums
ProjectionsScale Factors
County Coordinates
State Plane
UTM
Session Agenda
GNSS History & Basic Theory
Coordinate Systems/Calibrations
Setting up a Job
MNDOT VRS Recommendations
Resources Available
Questions?
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Learning Objectives
Fundamental understanding of GNSS
Confidently set-up a job
Increase productivity and reduce “down-time”
Maximize your investment
Find resources available
What is GNSS?
GNSS – Global Navigation Satellite System
This was originally called GPS – Global Positioning System
(which most people still refer to this term).
Now that there are many satellite vehicles (SV’S) and
systems in place, we refer to it as GNSS.
Systems:
• GPS (NAVSTAR–USA) 31 sv’s
• Glonass (Russian) 24 sv’s
• Galileo (European) 8 sv’s
• BeiDou (Chinese) 10 sv’s
• QZSS (Japan) 1 sv
• IRNSS (India) 3 sv’s
GPS/GNSS History
1959 - Navy built the first satellite navigation system.
Designed to locate submarines.
1963 - Aerospace Corporation completes military study
laying out the concepts for modern GPS.
1974 - Military launches the first of proposed 24-satellite
GPS system (NAVSTAR).
1985 - Government contracts with private companies
“man-pack portable” GPS receivers.
1990-2000 – Accuracy was decreased using Selective
Availability (turned off May 2000)
– military implications
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GPS/GNSS History
1995 – First Revision of the GPS system fully
completed. Full Constellation of 24 SV’s
1999 – Mobile phone GPS introduced in Europe
2000 – Selective Availability (SA) turned off
2012 – Air Force manages 31 operational GPS sv’s plus
3 decommissioned for future use. Phase II
2015 – RTX and xFill Technologies
March 28, 2015 – Galileo launches two SV’s (8 total)
GPS/GNSS Components :
Space segment
Control segment User segment
Space Segment
The space segment consist of a constellation of satellites
that transmit one-way signals that give the current satellite
position and time.
• Orbit the earth every 11 hours 58 minutes
• Altitude of 20,200km (12,552 miles)
• Six orbits spaced at 60 deg. apart
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Space Segment
Current GNSS Constellation• GNSS Satellites Launched from 1997 to 2012
Control Segment
The control segment consist of worldwide monitor and control
stations that maintain the satellites in their proper orbits and
adjust satellite clocks.
It tracks the GPS satellites, uploads navigational data, and
maintains health and status of the satellite constellation.
Master control stations
• GPS: Schreiver AFB – Colorado
• Glonass: Moscow, Russia
User Segment
The user segment consist of the GPS receiver equipment,
which receives the signals from the GPS satellites and uses
the transmitted information to calculate the user's three
dimensional position and time.
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How does GNSS measure?
Minimum of 4 satellites must be observed by both the base
and the rover. 5 required for an “over-determined” solution
Satellite Ranging:
Radio waves from satellites in conjunction with the exact
location of satellites based from atomic clocks and precise
orbits (space/control segment) determine distance from
satellite to base and rover.
Trilateration gives us our distance between the base and
rover.
Survey Requirements:
10:30 10:35
Code Phase vs. Carrier Phase
L1 = 19 cm
L2 = 24 cm
Carrier
Code
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Different Applications –Different Precisions
Standalone GPS: 5–10 m
DGPS: 0.5–1 m
VRS:1–2 cm
H-Star: 10–30 cm
Carrier Phase
• Interger Ambiguity – Initialization
• Required for cm accuracy solutions
What Real-Time sources
are Available?
• SBAS - WAAS
• Trimble RTX - OMNI-Star
• Single Base Real-Time
• VRS
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WAAS -Integrated
SBAS
<1–5 m <1–5 m
FREE – No Subscription Required
Compatible with all current
Trimble Handhelds
What Real-Time sources
are Available?
Trimble RTX and Omni- Star
0.1–5 m 0.1–5 m
Subscription Based
What Real-Time sources
are Available?
What Real-Time sources
are Available?
0.01–5 m 0.01–5 m
Single Base Real-Time
Corrections
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What Real-Time sources
are Available?
0.01–5 m 0.01–5 m
How can I receive corrections from a
single base provider solution?
What Real-Time sources
are Available?
0.01–5 m 0.01–5 m
How can I receive corrections from a
single base provider solution?
What Real-Time sources
are Available?
CORS GPS Network
0.01–5 m 0.01–5 m
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What does GNSS measure?
True/False It measures northing, easting and elevation.
FalseGNSS measures latitude, longitude and height of ellipsoid.
Ellipsoid – A mathematical ellipse approximating the shape
of the Earth. World Geodetic System 84 (WGS84)
Geoid models convert GNSS ellipsoid heights to North
American Vertical Datum 88 (NAVD88) orthometric
heights.
*Trimble software converts these numbers to northing, easting,
elevation based on Projections, Calibrations, Localizations, and Geoid
Models.
GNSS Coordinate Systems
• Earth Center Earth Fixed
• WGS 84
• Local Grid Coordinates
• State Plane (NAD83)
• MN County Coordinates
• UTM
• Local Grid
NEE
Types of Plane Systems –
Projections
Plane
Ellipsoid
Tangent PlaneLocal Plane
Point of Origin
Intersecting CylinderTransverse Mercator
Axis of Ellipsoid
Ellipsoid
Axis of Cylinder
Line of intersection
Apex of Cone
Intersecting Cone2 Parallel Lambert
Axis of Cone & Ellipsoid
Ellipsoid
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GNSS Heights vs. Elevations
GPS Measures Height - I want Elevation (MSL)
How do I get the best elevation from GPS?
Is it the proper tool to measure Elevation?
MN CORS VRS- Recommendations
• MN CORS Mount Points / Geoid Models
Looking further….
Whoever thought we would be talking about datum shifts…
Does WGS84 = NAD83?
Only with certain realizations: ie… NAD83(1986).
The Earth is under constant change and Geodesist are
measuring these changes and offering different
“realizations” to accommodate this.
Fundamental Awareness required.
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Know your Datums!
– Definition of Geodetic Datum“A geodetic datum is a set of constants specifying the coordinate system used for geodetic control”
– NAD83 is a Horizontal Control Datum• With multiple realizations
• NGS NOAA Tutorial on Datums
– NAD83 Relizations (1986, HARN, CORS 96, NSRS, 2011)
– NAD83 (2011) is the most current realization which all NGS CORS sites and NGS OPUS use
– How about VRS
– Does it Matter
Error Sources In GNSS
PDOP – “satellite geometry” < 6
RMS – “multipath” < 30
Ionosphere – upper atmosphere
Troposphere – lower atmosphere
Human Error
Which Error Source do we have no control over?
Trimble Access Job Settings
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Trimble Access Job Settings
Total Station Only
State Plane, County Coordinates, UTM
Enter Projection, Datum Tran., H & V adjustments
When performing calibration*
Long corridor (many km’s) railroads, pipelines, etc.
Coordinate system defined by broadcast
Coordinate Systems
Important Settings
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MN CORS VRS- Recommendations• MN CORS Mount Points / Geoid Models
Is a Performing a Site Calibration or localization Necessary?
With Pre-Defined Coordinate Systems (ie. County Coordinates):
Horizontal calibration should be one point only. More could alter the system.
Vertical calibration should be either one point or four or more with the geoid model.
Without A Pre-Defined Coordinate System:Horizontal Calibration should use three or more
points.Vertical calibration should be either one point or four
or more with the geoid model.
Note: remember that this can only be determined to any degree of certainty by actually measuring trusted control monuments in your area and examining the differences. Site Calibrations are also dependant on Project Accuracy requirements
Common Support Questions
Important to note in Minnesota when using VRS most counties except the Transverse Mercator counties, grid elevations equal ground level. Sea level
corrections should be unchecked as the grid has been “inflated” to ground level of each county. Orthometric heights grid/ground are essentially the same.
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Resources:
Support Blog Sites:• Geospatial Survey – www.fpisurvey.com
• Geospatial Mapping – www.fpimapping.com
• Webinars, Tech Talks, Procedure Sheets
Trimble Support:• www.trimble.com/support/support_AZ
• Software/firmware updates, latest versions, documentation
Geodetic Resources:• NGS
• OPUS – www.ngs.noaa.gov/OPUS
• Datums – Youtube Search
Certified Training – Highly Recommended:• Geospatial Survey
• Geospatial Mapping
• Web Based – watch out website (www.frontierprecision.com) or Blogs
Additional Resources:
IPhone/Android App – Product Resources,
Support, Training, Events and much more.
Questions?
Steve [email protected]