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GPS > Lect 06 Coordinate System > Flashcards

Lect 06 Coordinate System Flashcards

1
Q

What is a Coordinate System?

A

A standardized method for location codes (latitude/longitude, x/y axis)

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2
Q

How many types of coordinate systems are in GIS?

A
  • Geographic Coordinate System
  • Projected Coordinate System
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3
Q

In a coordinate system:

A

Easting is x direction (Longitude)
Northing is Y direction (latitude)

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4
Q

What happend if two map layers have different coordinate systems?

A

Problem: They will not align spatially
Solution: Standardize their coordinate systems

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5
Q

What is a geographic coordinate system?

A

*Locates features on earth using longitude and latitude.
* Measures angles in degree, degree-minutes-seconds (DMS), decimal degrees (DD), or radiands (rad)

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6
Q

Geographic Coordinate System

A

GCS range:
Latitude: 90º S to 90ªN
Longitude: 180ºW to 180 ºE

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7
Q

What are parallels:

A

Lines of constant latitude

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8
Q

What is a Meridian?

A

Lines of constant longitude

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9
Q

Difference between sphere and ellipsoid

A

The earth is often modeled as a sphere for map projections but it´s actually an ellipsoid with a larger equatorial radius

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10
Q

What is ellipsoidal?

A

A smooth average of the geoid, approximating earth´s shape that can differ from local sea level

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11
Q

What is Geoid?

A

*Surface of constant gravity
*Approximates local sea level with more variation than ellipsoid

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12
Q

What is ellipsoid height?

A

Height on an ideal surface used GPS and satellite imagery (NAD83)

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13
Q

What is Orthometric height?

A

Elevation above the geoid, used in surveying and land management eg., NAVD88.

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14
Q

What are the three commonly used ellipsoids?

A
  1. Clarke 1866
  2. GRS80 (Geodetic Reference System 1980)
  3. WGS84 (World Geodetic System 1984)
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15
Q

Why not the same ellipsoid?

A

Historically, geodetic surveys were limited by water bodies and relied on optical telescopes, constrained by Earth´s curvature.
Each continent had its tailored ellipsoidal parameters due to these isolated surveys.
Recently, satellite, laser, and timing signal data allow for precise global position measurements across continents and oceans.

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16
Q

What is Datum?

A

A mathematical earth model, foundational for geographic coordinates.

Defines Earth´s size, shape, origin, and mapping orientation.

Determined by an ellipse and rotation axis, it comprises:
1. Ellipsoid parameters and origin
2. Points and lines set

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17
Q

What are the two types of Datum?

A

Geocentric datum (x, y)
Based on ellipsoid (e.g., NAD8, WGS84)
cf. NAD27 is a local datum

Vertical Datum
References the geoid (e.g., NAVD88)

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18
Q

What are benchmarks?

A

Points surveyed during datum development and marked with monuments

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19
Q

What is vertical datum?

A

Horizontal control networks
* Provide positional data related to a mathematical surface (e.g ellipsoid).
*Vertical Control Networks
* This elevation, called orthometric height, is determined by spirit leveling with gravity measurements.

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20
Q

What are the main horizontal datums?

A

1) North Americam Datum 1927 (NAD27)
2) North American Datum 1983 (NAD83)

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21
Q

What is Map Projection

A

Converting a three dimensional surface (like earth) to a two dimensional (flat) surface

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22
Q

What are some of the advantages of Map Projection?

A
  1. Allows for 2D paper and digital maps over globes.
  2. Uses plane coordinates instead of longitude & latitude.
  3. Offers straightforwraddistance and area measuraments compared to GCS.
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23
Q

Distorition in Map Projection

A

1) Map projection always have errors and spatial distortions.
2) The right projection preserves properties and reduces distortions in targeted areas.

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24
Q

Four properties for preservation

A
  1. Conformal (Shape)
  2. Equivalent (Area)
  3. Equidistant (Distance)
  4. Azimuthal (Direction)
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25
Q

Azimuthal

A

For global views

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26
Q

Cylindrical (Transverse Mercator)

A

For North-South Areas

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27
Q

Conic (Albers, Lambert Conformal)

A

For East-West areas

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28
Q

State Plane Coordinate System

A

Based on state and county geography

Used for legal boundaries in civilian systems

Ensures top local measurements accuracy

120 Zones, shaped by state and zone contours

29
Q

Global Correction Service (IGS)

A

Operates a global network of over 512 tracking stations.
 A voluntary group of more than 350 agencies producing precise GPS/GLONASS products.
 Committed to top-quality data, setting GNSS standards.

30
Q

RINEX (Receiver Independent Exchange Data Format) - IGS

A
  • A standardized format by IGS (Used for archiving and online access at the global data center)
  • With accuracy level depending on availabilty
31
Q

Regional Correction Services

A
  • CORS (Continuously Operating Reference Station)
    1. United States.
    2. Over 2,000 continuously operating stations.
    3. Providing GPS measurements for 3D positioning.
32
Q

Regional Correction Services

A

CACS (Canadian Active Control System)
 Canada
 Operates continuously.
 With over 135 stations.
 Offers real-time positioning accuracy within one meter and post-processing accuracy within three centimeters.
 Both CORS and CACS stations are closer to the reference stations than the IGS stations.

33
Q

DGPS Radio Beacon System

A

Marine radio beacons at lighthouses
and coastal locations are electronic
navigation aids operating in the low-to-
medium frequency band (283.5-325
kHz).

34
Q

DGPS Radio Beacon System

A

A reference station (RS) generates real-
time DGPS corrections in the RTCM (Radio
Technical Commission for Maritime
Services) format.
 With an integrity-monitoring (IM) unit
overseeing its performance.
 Free for all users.

35
Q

RTCM (Radio Technical Commission for Maritime Services) Format

A

 Coastal networks of reference stations.
 Continuously transmits real-time DGPS corrections with the
RTCM format.
 Enhancing marine navigation safety.
 A beacon receiver connected to a GPS receiver that accepts RTCM corrections is needed to use this service.

36
Q

RTCM (Radio Technical Commission for Maritime Services) Format

A

 GPS receivers that accept RTCM corrections are known as
differential-ready GPS receivers.
 Offering accuracy from sub-meter to a few meters.
 Free for the general public.

37
Q

Radio Beacon Receiver

A

Combination of Beacon/GPS Receiver:
 Micro-Trak T100
 Single Unit
 DGPS Radio Beacon Receiver:
 Trimble beacon-on-a-belt (bob)

38
Q

DGPS Radio Beacon System

A

 These receivers pick up the transmitted DGPS corrections and come in single- or dual-channel options, with dual-channel being more reliable but pricier.
 The official range is 150 miles, as per the Coast Guard.
 Coverage depends on factors like transmitter power output, atmospheric
noise, receiver sensitivity, and propagation characteristics, which are better
over water than inland areas.
 Beacon locations are strategically selected for overlapping coverage to
enhance accuracy.

39
Q

DGPS Radio Beacon System

A
  • Differential corrections come from the NAD 83 position of the reference station (REFSTA) antenna, so DGPS positions should align with the NAD 83 coordinate system.
40
Q

WADGPS (Wide Area DGPS) Systems

A
  • A satellite-based differential correction service
  • Using widely separated reference stations
  • Providing sub-meter accuracy
  • Utilizing the RTCA (Radio Technical Commision for Aeronautics) format for aviation telecommunications
41
Q

WADGPS (Wide Area DGPS) Systems

A

 Real-time DGPS with a single reference station faces the challenge of declining accuracy:
(1) Users moves farther from the reference station.
(2) With the highest accuracy limited to a small area around the reference station.
 Fix: WADGPS is employed.

42
Q

WADGPS Systems

A

Steps outlining how the WADGPS system
operates:
1.Reference stations
 Gather the GPS data and transmit it to the
master station.
2.Master station
 Analyzes correction data and uploads it to a
geostationary satellite.
3.Geostationary satellites
 Transmit the data to a local GPS receiver.
4.GPS receiver
 Applies the necessary corrections.

43
Q

WADGPS Systems

A

WADGPS includes four satellite-based augmentation systems:
1. WAAS (Wide Area Augmentation System) in North America
2. EGNOS (European Geostationary Navigation Overlay System)
in Europe
3. MSAS (Multi-Functional Satellite Augmentation System) in Asia
– Japan
4. GAGAN (GPS and GEO Augmented Navigation) in Asia - India

44
Q

Geostationary Satellite

A

 A geostationary satellite, or GOES (Geostationary Operational Environmental Satellite).
 Orbits the earth at the same rate as its rotation.
 Maintaining a fixed positioning over the equator.

45
Q

Geostationary Satellite

A

 Often called TV satellite.
 Completes a 24-hour orbit that matches the Earth’s rotation.
 In contrast, GPS satellites orbit twice a day, finishing their orbit in 12 hours.

46
Q

Satellite Orbit

A
  1. Low Earth Orbit: Sun - Synchronous
  2. Medium Earth Orbit: Semi-synchronous
  3. High earth orbit: geo-synch
47
Q

WAAs VS. LAAS

A

Both WAAS and LAAS are GPS augmentation systems that enhance accuracy, availability, and integrity.
 WAAS (wide-area augmentation systems) is satellite-based.
 LAAS (local-area augmentation systems) is ground-based.

48
Q

WAAS (Wide - Area Augmentation Systems)

A

 A Space Base Augmentation System (SBAS) supported by the FAA and DOT.
 Specifically implementing WADGPS.
 Enchains GPS signal accuracy.
 Initially designed for civil aviation, its coverage now extends to inland and
offshore areas, making it suitable for land and marine applications.
 Continental DGPS systems are limited to North America due to no ground
reference stations elsewhere

49
Q

WAAS (Wide - Area Augmentation Systems)

A

 Pros: WAAS requires no additional receiving equipment and offers broader coverage, including inland and offshore areas, compared to land-based DGPS.
 Cons: Signal reception can be hindered by obstructions like trees or mountains due to the satellite positions over the equator.

50
Q

WAAS - How does it work?

A
  1. Ground stations: Collect GPS data and send it to the master station.
  2. Master station: Analyzes correction data and uploads it to a geostationary satellite
  3. Geostationary satellites: Transmits data to a local GPS receiver.
  4. GPS receiver: Apply the appropriate correction.
51
Q

WAAS - Accuracy

A
  • Differential corrections provided by WAAS increases the accuracy of C/A signals.
52
Q

LAAS (Local Area Augmentation System)

A
  • Achieves higher accuracy through local-area base stations.
  • Operates on a smaller scale
  • Reference receivers near runways provide significantly more accurate correction data to incoming planes
53
Q

LAAS (Local Area Augmentation System)

A

Are located near airports
Broadcast correction messages within a limited range of 20-30 miles.
Uses a VHF (very high frequency) radio data link
LAAS accuracy is less than one meter

54
Q

LAAS Air Navigation

A
  • Reference receivers, positioned close together,
    collect measurement errors.
  • They broadcast correction messages via a VHF
    (Very High Frequency) radio data link
55
Q

Why integration with GPS?

A

 GPS applications enhance accuracy and global availability.
 However, they face signal obstruction in some scenarios.
 e.g., urban canyons and deep open-pit mining
 Solution: Integration of GPS with other positioning systems

56
Q

GPS Integration

A

 To overcome signal obstructions, GPS is integrated with other
systems like:
1. GIS
2. LORAN (Long-Range Navigation)
3. LRF (Laser Range Finder)
4. Dead Reckoning
5. INS (Inertial Navigation System)
6. Pseudolite
7. Cellular systems

57
Q

GPS/GIS Integration

A

 GPS efficiently collects precise GIS field data in digital format, in real-time or post-processed.
 GPS-GIS integration serves various industries.
 e.g., utilities, forestry, agriculture, and public safety

58
Q

GPS/GIS Integration: Mobile GIS

A

Trimble Juno SB
* Offers a positioning
accuracy of 2 to 5
meters in real time and
1 to 3 meters when
post-processed.

59
Q

GPS/Loran-C Integration

A

LORAN (Long-Range Navigation) is a terrestrial radio-navigation system with master and secondary stations

The LORAN system was phased out in 2010

60
Q

GPS/LRF Integration

A

 GPS signals under tree covers are challenging.
 Solution: LRFs (Laser Range Finders)
 Post-processing is needed to combine the data.

61
Q

GPS/LRF Integration

A

 When:
 In inaccessible under tree canopies
 In areas with poor GPS visibility
 How:
 Set up a GPS antenna in a clear-sky open area
 Use an LRF to determine distances and azimuth to objects
 Offset function: Records feature offsets while staying in one
spot

62
Q

GPS/LRF Integration

A

 Applications
 Utility industry:
 e.g., electric, gas, and water utility
companies
 Forestry and natural resource
 e.g., fire prevention, control/harvesting
operations, insect infestation, boundary
determination, and aerial spraying
 10.14  Cadastral surveying
 e.g., establishing property corners,
boundaries, and areas of land parcels.

63
Q

GPS/DR Integration

A

 The Dead Reckoning (DR) system supplements GPS in areas with poor signal reception.
 It estimates position from a known point using factors (e.g.,
direction, speed, time, and distance).
 DR is cost-effective, using:
 Odometer sensors (measure vehicle distance/speed)
 Vibration gyroscopes (measure vehicle direction with low-
cost angular rate sensors)

64
Q

GPS/DR Integration

A

 When:
 In urban areas where, GPS quality is vital, but obstructed by
buildings
 How:
 Use the odometer for distance and gyroscope for direction
 Limitations:
 GPS unavailable in obstructed areas
 DR drifts over time, causing positional errors.

65
Q

GPS/DR Integration

A

 In vehicle location & navigation:
 GPS helps calibrate DR, which serves as the main system
during GPS failures.
 GPS/DR integration provides better estimates for positioning
and direction.
 However, it is NOT ideal for high-accuracy applications.

66
Q

GPS/INS Integration

A

Mining and airborne mapping need high-accuracy positioning in
obstructed or dynamic conditions due to GPS limitations.
Solution: GPS/INS integration
Inertial Navigation System (INS) use inertial sensors (IMU) to
determine vehicle position, velocity, and orientation.
INS is environment-independent, jamming-resistant, and more
accurate than dead reckoning (DR).

67
Q

GPS/INS Integration

A

 An INS includes accelerometers (measuring acceleration) and
gyroscopes (measuring rotational velocity).
 Once initialized, it provides 3-D position and velocity
autonomously.
 Drawback: Drift over time, causing unbounded errors if unaided.

68
Q
A

GPS (9 decks)

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