Introduction to GPS

Presented by:

WELCOME

• Introductions – Scott Hill PLS, PMP• Expectations• What is Land Surveying?• Class Material to be Covered

– Coordinate Systems– GPS Principles– GPS Surveying– Survey Tools– Field Exercise– Classroom Exercise

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What is Land Surveying, and a Land Surveyor?

• Classical Definition– The use of the principles of mathematics to

establish the location of Real Property Boundaries or points on the ground.

• Usually defined by statute.– Nevada

• NRS 625.040 - NRS 625.070– Arizona

• ARS 32-101.22 - ARS 32-101.23– California

• California Business and Professional CodeSection 8726-8731

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Coordinate Systems

• Assumed Coordinate Systems• Map Projections• Geodetic Datums

– Global Coordinate Systems– UTM – Universal Transverse Mercator– ECEF – Earth Fixed, Earth Centered– NAD 83– SPC – State Plane Coordinates

• HARN• CORS

Coordinate Systems

• Assumed Coordinate Systems– Cartesian Coordinates based on x,y,z

axis– Northing (y), Easting (x), Elevation (z)

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Coordinate Systems

Map Projections

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Coordinate Systems-Projections

• MercatorThe Mercator projection has straight meridians and parallels that intersect at right angles. Scale is true at the equator or at two standard parallels equidistant from the equator. The projection is often used for marine navigation because all straight lines on the map are lines of constant azimuth.

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• Transverse MercatorTransverse Mercator projections result from projecting the sphere onto a cylinder tangent to a central meridian. Transverse Mercator maps are often used to portray areas with larger north-south than east-west extent. Distortion of scale, distance, direction and area increase away from the central meridian. Used by USGS for many quadrangle maps at scales from 1:24,000 to 1:250,000; such maps can be joined at their edges only if they are in the same zone with one central meridian.

Coordinate Systems-Projections

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• Lambert Conformal ConicUsed by USGS for many 7.5- and 15-minute topographic maps and for the State Base Map series. Also used to show a country or region that is mainly east-west in extent. One of the most widely used map projections in the United States today. Distances true only along standard parallels; reasonably accurate elsewhere in limited regions. Directions reasonably accurate. Distortion of shapes and areas minimal at, but increases away from standard parallels. Shapes on large-scale maps of small areas essentially true.

• RobinsonUses tabular coordinates rather than mathematical formulas to make the world "look right." Better balance of size and shape of high-latitude lands than in Mercator. Directions true along all parallels and along central meridian. Distances constant along Equator and other parallels, but scales vary. All points have some distortion. Very low along Equator and within 45° of center. Greatest near the poles. Used in Goode's Atlas, adopted for National Geographic's world maps in 1988, appears in growing number of other publications, may replace Mercator in many classrooms.

Coordinate Systems

• Geodetic Datums – Geodetic datums define the reference systems that describe the size and shape of the earth.

Hundreds of different datums have been used to frame position descriptions since the first estimates of the earth's size were made by Aristotle. Datums have evolved from those describing a spherical earth to ellipsoidal models derived from years of satellite measurements.

– Modern geodetic datums range from flat-earth models used for plane surveying to complex models used for international applications which completely describe the size, shape, orientation, gravity field, and angular velocity of the earth. While cartography, surveying, navigation, and astronomy all make use of geodetic datums, the science of geodesy is the central discipline for the topic.

– Referencing geodetic coordinates to the wrong datum can result in position errors of hundreds of meters. Different nations and agencies use different datums as the basis for coordinate systems used to identify positions in geographic information systems, precise positioning systems, and navigation systems. The diversity of datums in use today and the technological advancements that have made possible global positioning measurements with sub-meter accuracies requires careful datum selection and careful conversion between coordinates in different datums.

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Coordinate Systems

• Geodetic Datums– Global Coordinate System– UTM– Earth Fixed, Earth Centered– State Plane Coordinate System

• HARN• CORS

Coordinate Systems

• Global Coordinate Systems– The most commonly used coordinate system today

is the latitude, longitude, and height system. – The Prime Meridian and the Equator are the

reference planes used to define latitude and longitude.

– The geodetic latitude (there are many other defined latitudes) of a point is the angle from the equatorial plane to the vertical direction of a line normal to the reference ellipsoid.

– The geodetic longitude of a point is the angle between a reference plane and a plane passing through the point, both planes being perpendicular to the equatorial plane.

– The geodetic height at a point is the distance from the reference ellipsoid to the point in a direction

normal to the ellipsoid.

Coordinate Systems

• UTM Coordinates - Universal Transverse Mercator

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Coordinate Systems

• UTM – Universal Traverse Mercator Coordinate System

The UTM system was an attempt to set up a universal world wide system for mapping. The Transverse Mercator projection is used, with the cylinder in 60 positions. This creates 60 zones around the world. Positions are measured using Eastings and Northings, measured in meters, instead of Latitude and Longitude. Eastings start at 500,000 on the centre line of each zone. In the Northern Hemisphere, Northings are zero at the equator and increase northward. In the Southern Hemisphere, Northings start at 10 million at the equator, and decrease southward. You must know which hemisphere and zone you are in to interpret your location globally.  Distortion of scale, distance, direction and area increase away from the central meridian.Put another way:  UTM projection is used to define horizontal positions world-wide by dividing the surface of the Earth into 6 degree zones, each mapped by the Transverse Mercator projection with a central meridian in the center of the zone. UTM zone numbers designate 6 degree longitudinal strips extending from 80 degrees South latitude to 84 degrees North latitude. UTM zone characters designate 8 degree zones extending north and south from the equator. Eastings are measured from the central meridian (with a 500 km false easting to insure positive coordinates). Northings are measured from the equator (with a 10,000 km false northing for positions south of the equator). UTM is applied separately to the Northern and Southern Hemisphere, thus within a single UTM zone, a single X / Y pair of values will occur in both the Northern and Southern Hemisphere. To eliminate this confusion, and to speed location of points, a UTM zone is sometimes subdivided into 20 zones of Latitude.  These grids can be further subdivided into 100,000 meter grid squares with double-letter designations. This subdivision by Latitude and further division into grid squares is generally referred to as the Military Grid Reference System (MGRS).The unit of measurement of UTM is always meters.The zones are numbered from 1 to 60 eastward, beginning at the 180th meridian.  Some software uses negative zone numbers to indicate that the data is in the southern hemisphere, e.g. zone 19 is north of the equator, zone -19 is south of the equator.

Coordinate Systems

• Earth Centered, Earth Fixed (ECEF) Coordinates– Earth Centered, Earth Fixed Cartesian

coordinates are also used to define three dimensional positions.

– Earth centered, earth-fixed, X, Y, and Z, Cartesian coordinates (XYZ) define three dimensional positions with respect to the center of mass of the reference ellipsoid.

– The Z-axis points toward the North Pole. – The X-axis is defined by the intersection of the

plane define by the prime meridian and the equatorial plane.

– The Y-axis completes a right handed orthogonal system by a plane 90 degrees east of the X-axis and its intersection with the equator.

Coordinate Systems

• NAD 83Official datum used for the primary geodetic network in North America.

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Coordinate Systems

• State Plane Coordinates

– In the United States, the State Plane System was developed in the 1930s and was based on the North American Datum 1927 (NAD27).

• NAD 27 coordinates are based on the foot. • While the NAD-27 State Plane System has been superseded by the NAD-83 System, maps in

NAD-27 coordinates (in feet) are still in use. • Most USGS 7.5 Minute Quadrangles use several coordinate system grids including latitude and

longitude, UTM kilometer tic marks, and applicable State Plane coordinates. • The State Plane System 1983 is based on the North American Datum 1983 (NAD83). • NAD 83 coordinates are based on the meter.

– State plane systems were developed in order to provide local reference systems that were tied to a national datum.

– Some smaller states use a single state plane zone. – Larger states are divided into several zones. – State plane zone boundaries often follow county boundaries. – Lambert Conformal Conic projections are used for rectangular zones with a larger east-west than north-

south extent. – Transverse Mercator projections are used to define zones with a larger north-south extent. – One State Plane zone in Alaska uses an oblique Mercator projection for a thin diagonal area.

Coordinate Systems

• State Plane Zones– NV & AZ

• East, Central, West• Traverse Mercator

– CA• Zones I through VI • Lambert Conic

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Coordinate Systems

• Nevada SPC Zones

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Coordinate Systems

• Arizona SPC Zones

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Coordinate Systems

• California SPC Zones

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Coordinate Systems

• HARN - High Accuracy Reference Network

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Coordinate Systems

• CORS-Continuously Operating Reference Stations

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Coordinate Systems

• CORS-Continuously Operating Reference Stations

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Coordinate Systems

• Grid to Ground Scaling

GPS Surveying

• When did this all start?• Satellite Navigation began in 1958.

• NAVSTAR’s first satellite in 1978.

• GPS fully operational in 1993.

GPS Surveying

• The 3 Parts of GPS1) Space Segment – the satellite network.

2) Control Segment – ground stations.

GPS Surveying

• The 3 Parts of GPS

3) User Segment – basically “You”.

GPS Surveying

• How it works?

Time = Distance

Simply Stated…….

GPS Surveying

• GPS Applications• Survey Grade GPS Equipment

- Centimeter Positioning

• GIS Mapping - Hand Held GPS

- Sub-Meter Positioning

GPS Surveying

• GPS Surveying Techniques

• Static Surveys

• Rapid Static Surveys

• Kinematic Surveys

• Post Processed Kinematic (PPK)

• Real Time Kinematic (RTK)

• Airborne GPS (ABGPS)

GPS Surveying

• The “Key” to a successful GPS Survey

• Planning• Network Configuration

• PDOP Graphing

• Site Recon

• CORS Stations

• GPS Survey Method

GPS Surveying

• Primary Sources of Error on a GPS Survey

• Instrument Errors• Clock Bias

• Set-up Errors

• Non-Parallelism of the Antenna

• Selective Availability

• Receiver Noise

GPS Surveying

• Primary Sources of Error on a GPS Survey

• Natural Errors• Ionospheric Refraction

• Tropospheric Refraction

• Relativity

• Multipath

GPS Surveying

• Primary Sources of Error on a GPS Survey

• Personal Errors• Tripod Mis-centering

• Mis-read Antenna Height

• Mis-identified Antenna Type

• Incorrect Station I.D.

• Processing Trivial Baselines

Survey Equipment

• Compass• Transit• Chain• Level• Total Station• GPS Receiver• Data Collector

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Survey Equipment

• Compass

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Survey Equipment

• Transit

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Survey Equipment

• Chain

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Survey Equipment

• Theodolite

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Survey Equipment

• Level

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Survey Equipment

• Total Station

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Survey Equipment

• GPS Receiver

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Survey Equipment

• Data Collector

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Survey Equipment

• GIS Handheld GPS

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Field Exercise

• Map Reference• Equipment Set-up• Survey Measurements• Data Collection• Survey

Reporting/Product

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Field Exercise

• Map Reference

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Field Exercise

• Equipment Set-up

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Field Exercise

• Survey Measurements

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Field Exercise

• Data Collection

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Field Exercise

• Survey Reporting/Product

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Classroom Exercise

• Download field data• Mapping field data

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Classroom Exercise

• Download field data

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Classroom Exercise

• Mapping field data

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Questions

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