High Precision GNSS for Mapping & GIS Professionals
High Precision GNSS for Mapping & GIS Professionals
Agenda• Address your needs for GNSS knowledge.• GNSS Basics• Satellite Ranging Fundamentals (Code $ Carrier)• Differential Corrections (Post‐Processed $ Real‐Time)• Real‐Time Corrections (Radio & Cellular)• GNSS System Components• Geodesy 101• Are you practicing Land Surveying? The Gray Area.
Your Needs for GNSS Knowledge
• Who’s using it? (You/Coworkers)• What kind of unit/precision? (10m or 10cm)• Where are you using it? (Locally/Remotely)• When are you using it? (Daily Use/Project Specific)• Why are you using it? (Requirement/Value Added)• How are you using it? (Business Line/Application)
GNSS: Global Navigation Satellite System
GNSS: Global Navigation Satellite System
NAVSTAR GLONASS
The Constellations• NAVSTAR aka GPS (United States DoD)
– 31/36 (Block III)
• GLONASS (Russian Federation)– 24/27
• Galileo (European Union)– 11+4+3/30
• BeiDou aka Compass (People’s Republic of China)– 21/35
• QZSS (Japan Regional) “We might be able to use this.”• IRNSS (Indian Regional Navigation Satellite System)
So… that’s cool, but how do we get PRECISION???
We must know where the satellite is, and we must determine the distance to it. We refer to this as
satellite RANGING.
Four Satellite Minimum (X, Y, Z, Time)
Code Ranging
Measurement of time difference between the same part of code.
To Receiver
From Satellite
Distance = Speed Of Light x Time Difference
Carrier Ranging
= First Partial WavelengthN = Integer Ambiguity
Solving for the integer ambiguity yields centimeter precision.
So… that’s cool, but how do we get PRECISION???
We must have a second receiver on a “known” point. From this
receiver second, we can generate a DIFFERENTIAL correction.
CORSOur gateway to accessing the National
Spatial Reference System
AGC Geodetic Control
Real‐Time Correction ComparisonRADIO CELLULAR DATA
Limited Range Limited to Cell Availability
Relies on a Battery Requires a cellular data plan
Requires a FCC License May require subscription.
Limited by baseline length… Allows for Multi‐Station Solution (Better)
More Equipment / Investment
Less Equipment / Typically 60% Investment vs Radio.
Rover Receiver
Rover Radio Antenna
Data Collector
Rover Pole
Bipod
xxxxx
Base Receiver
Tribrach
Base Receiver Battery
Radio Data Cable
Base Receiver Tripod
Data CollectorBase Radio
Battery
Base Radio
Base Radio Tripod
Antenna Cable
Radio Antenna
So… that’s cool, but how do we get ACCURACY???
1. Use a High Precision GNSS Receiver2. Use Proper Field Procedures3. Apply sound Geodetic Principles
Earth‐Centered Earth‐Fixed (ECEF)Ellipsoid(e.g., GRS‐80, WGS‐84) +Z axis (parallel to axis of rotation)
+X axis(Prime meridian)
–Y axis (90°W)
–Y1
+Z1
Earth mass center–X1–X axis
(180°W)
+Y axis (90°E)
–Z axis
Equatorial plane
λ1
φ1
h1
Coordinates:(–X1, –Y1, +Z1)(φ1, λ1, h1)
Geoid(“mean sea level”)
p4
Anchorage
PUBLIC SERVICE ANNOUNCEMENTS:
WGS84 IS NOT THE SAME AS NAD83
PUBLISHED LATITUDES & LONGITUDES ON PUBLIC DATA SOURCES SHOULDREFERENCE NAD83… BE WEARY.
ALASKA: US SURVEY FEET
Relationship between the MANY ‘flavors’ of nad83 and GNSS‐derived NAVD88 HEIGHTS
All hybrid geoid models from NGS are intended for use with NAD83, but for the most consistent results, ensure that the geoid model used matches the correct ‘flavor’ of NAD83
Alaska: For NAD83(1986) use Geoid06
For NAD83(2007), NAD83(CORS96) use Geoid09
For NAD83(2011) use Geoid 12A/B
NAD83(2007)
NAD83(2011)
NAD83(1986)
NAD83(1997)
NAD83(2011)
Birth: NAD83(1986) Differential leveling only1st adjustment NAD83(1997) GNSS/HARN and more leveling also: NAD83(HARN)
NAD83(CORS96) GNSS/CORS (2007.00 epoch in AK)2nd adjustment NAD83(2007) GNSS/CORS3rd adjustment NAD83(2011) CORS
Note: for Alaska these are the only three
hybrid geoid models that exist
Adjustments to the National Spatial Reference System (NSRS)
THE GEOID FOR ALASKA: GEOIDxx
SPCS vs. UTM
SPCS: 1 in 10,000UTM: 1 in 2500
AS 08.48.341.(13) "practice of land surveying" means the teaching of land surveying courses at an institution of higher learning, or any service or work the adequate performance of which involves the application of special knowledge of the principles of mathematics, the related physical and applied sciences, and the relevant requirements of law for adequate evidence of the act of measuring and locating land, geodetic and cadastral surveys for the location and monumentation of property boundaries, for the platting and planning of land and subdivisions of land, including the topography, alignment, and grades for streets, and for the preparation and perpetuation of maps, record plats, field note records, and property descriptions that represent these surveys;