Continuously Operating Reference Stations CORS - PowerPoint PPT Presentation

1 / 117
About This Presentation
Title:

Continuously Operating Reference Stations CORS

Description:

Continuously Operating Reference Stations CORS – PowerPoint PPT presentation

Number of Views:1494
Avg rating:5.0/5.0
Slides: 118
Provided by: russ73
Category:

less

Transcript and Presenter's Notes

Title: Continuously Operating Reference Stations CORS


1
(No Transcript)
2
Continuously Operating Reference Stations (CORS)
  • Overview of Height Modernization Project
  • Definition of CORS
  • Different uses of CORS
  • CORS Datum

3
Alabama Height Modernization
  • Funding from Congress for Alabama sponsored by
    Congressman Cramer
  • Program managed by Department of Commerce NOAA
    - NGS
  • Alabama Department of Revenue is grant recipient
  • Surveying Tasks Delegated to Alabama Department
    of Transportation

4
What is Height Modernization?
Wisconsin Height Modernization Project
5
(No Transcript)
6
Height Modernization Activities assigned to ALDOT
  • GPS Surveys using procedures from NOS NGS 58 59
    2 cm repeatable elevations from GPS.
  • First and Second Order Leveling to support NOS
    NGS 58 59 Surveys and to restore and verify
    lines throughout the state.
  • CORS Establish a state-wide CORS network to
    serve as the National Spatial Reference System
    (NSRS) for the state in the future and to provide
    data for monitoring crustal motion See
    Louisiana and NOS 50 4-D Positioning

7
GPS
  • GPS projects are performed using the NOS NGS 58
    59 procedures to obtain 2 cm heights.
  • Primary Base Network A Order Horizontal and
    vertical marks observed on a 40 to 50 kilometer
    grid. Three 5 ½ hour sessions.
  • Secondary Base Surveys in 9 areas of the state.
    Observations are complete and data is being
    processed. Final processing will be completed
    when leveling is completed. New and existing
    marks observed on a 12 to 15 kilometer grid.
    Emphasis on vertical component and 2 cm
    repeatability on GPS elevations.
  • Local Base Surveys Basically the same
    procedures as the Secondary Base Surveys on a 4
    to 6 kilometer grid.
  • Re-establish Azimuth mark for A Order project
    Back azimuth or mate was not observed and has
    resulted in azimuth errors on the ground.
    Preliminary planning is underway to re-establish
    all of the azimuth mates to the new A order marks.

8
2003
9
2006
10
Goals
  • Primary Base Network Horizontal and vertical
    marks established on a 40 to 50 kilometer grid.
    Attempt was made during reconnaissance to utilize
    as many benchmarks as possible. Leveling
    projects will place elevations on the remaining
    marks so that each A order mark has a first or
    second order elevation. These marks will be the
    foundation for the NOS NGS 58 59 surveys.
    Leveling began in May 2005 in Southeast Alabama
    (Dothan area).
  • More good elevations on good GPS Marks better
    Geoid Model. Once leveling is complete to the
    Primary Marks, we will request that NGS define a
    new Geoid Model for Alabama.
  • Better Geoid Model Better GPS elevations

11
(No Transcript)
12
Leveling Objectives
  • Put good NAVD 88 Heights on good Horizontal Marks
    observed with GPS
  • Place good NAVD 88 Heights on CORS Antenna
    Reference Plane or ARP.
  • Extend Leveling to areas with poor/non-existent
    benchmarks.

13
Reconnaissance shows that up to 2/3 of Benchmarks
are destroyed or cannot be found!
14
Leveling Projects to support Primary and
Secondary GPS Projects
  • 44 miles Monroe, Clarke Escambia
  • 20 miles Dallas, Lowndes
  • 48 miles Marion, Franklin
  • 10 miles Lawrence, Limestone
  • 15 miles Talladega, Clay
  • 34 miles Elmore, Montgomery
  • 14 miles Macon
  • 30 miles Coffee, Geneva, Henry
  • 85 miles Remaining Primary Marks
  • 340 miles total

15
Leveling Projects to CORS stations
  • Second Order Class I leveling to the Antenna
    Reference Plane (ARP) of the CORS
  • Field work is complete for Huntsville, Tuscumbia,
    Birmingham, Tuscaloosa, Auburn, and Troy
  • Preliminary planning underway for Alex City,
    Montgomery, Dothan, and Mobile.
  • Establish NAVD 88 Orthometric Elevations at each
    CORS station.

16
CORS
  • Continuously Operating Reference Stations CORS
  • Permanently mounted dual frequency GPS receivers
    connected to a recording device and operates 24
    hours a day, 7 days a week, 52 weeks a year with
    the raw data available via the internet and Real
    Time corrections available via wireless cell
    modem, radio signal, or both.

17
  • The Global Positioning System (GPS) is a set of
    satellites that enable you to determine your
    position anyplace on earth, 24-hours a day
    regardless of the weather
  • The system consists of 24 operational satellites
    and four non-operational spare satellites
    orbiting 12,000 miles above the earth
  • The satellites are arranged so that several
    satellites are always in view from any point on
    earth.
  • The Global Positioning System (GPS) is based on
    the Department of Defense NAVigation Satellite
    Timing and Ranging (NAVSTAR) satellites.
  • The service is free and is provided 24 hours a
    day world wide.
  • GLObal NAvigation Satellite Systems (GLONASS) is
    provided by the Russian Federation
  • European Galileo system is currently being
    developed and will add a third set of satellites.

18
GPS Space Segment
  • 24 Operational satellites (28 on orbit)
  • Six orbital planes at an altitude of 12,600
    statute miles
  • Satellites are spaced in orbit so that a minimum
    of five satellites will be in view to users
    worldwide
  • Each satellite completes an orbit once every 12
    hours and will pass over head twice a day.

19
Global Positioning SystemGPS
20
(No Transcript)
21
Uncorrected GPS
  • Hand held receivers
  • Personal Digital Assistant (PDA) systems
  • Lap Top based computer systems
  • Uses code (L1) information
  • Does not need base station or corrections
  • Accuracies between 6 and 11 meters

22
GPS Modernization Plan
Block III
Block IIR-M, IIF
Block IIA/IIR
  • III IIF capabilities
  • Improved civil signal (L1C)
  • Increased accuracy (4.8-1.2m)
  • Evaluating integrity improvements
  • Navigation surety for military
  • Increased A/J power (20 dB)
  • IIR-M IIA/IIR capabilities
  • 2nd civil signal (L2C)
  • New military code
  • Flex A/J power (7dB)
  • IIF IIR-M capability plus
  • 3rd civil signal (L5)
  • IIA / IIR Basic GPS
  • C/A civil signal (L1C/A)
  • Std Service, 16-24m SEP
  • Precise Service, 16m SEP
  • L1 L2 P(Y) nav

23
Basic Civil Positioning Before May 2000
100 m
GPS I, GPS II A, GPS II R
  • C/A Code on L1
  • Selective Availability On

24
Basic Civil Positioning Now
6-11 m
GPS II R
  • C/A Code on L1
  • Selective Availability Off

25
Basic Civil Positioning By 2009
3-5 m
GPS II R(M)
  • C/A Code on L1
  • Civil Code on L2

26
Basic Civil Positioning By 2014
Better resistance to interference
1-3 m
GPS II F
  • C/A Code on L1
  • Civil Code on L2
  • New Code on L5

27
Basic Civil Positioning 2018
?
GPS III Full Operational Capability
28
(No Transcript)
29
Differential or Static GPS Surveys
  • Dual frequency GPS receiver tracks CA code,
    carrier and L1, L2
  • Needs minimum of five satellites for
    initialization, then four
  • Must have one or more base stations occupying
    known positions
  • 1-2 centimeters IF proper procedures are followed.

30
Why CORS?
  • One Base Station for an area can serve many
    projects
  • Reduced personnel and equipment costs
  • Consistent coordinate datum
  • CORS will eventually be National Spatial
    Reference System (NSRS)

31
CORS Group
  • Alabama Society of Professional Land Surveyors -
    ASPLS
  • Geospatial Training and Application Center GTAC
  • Troy University Geomatics Program
  • GPS users in the First, Second, and Fifth
    Divisions

32
Why would ALDOT maintain the CORS Network?
  • Secure facilities throughout the state.
  • Long term commitment to maintain sites.
  • Each facility has generator back-up power in the
    event of outages
  • Each facility has a T1 line for data transmission
  • Each Division has IT personnel to assist in the
    maintenance of the stations.
  • CORS network could be easily absorbed by ALDOT at
    a lower cost.

33
Objectives for a CORS Network
  • Short Term
  • Improve coverage for Static GPS Work
  • Leveling to establish NAVD 88 Orthometric Heights
    at the Antennae Reference Plane (ARP)
  • Long Term
  • State-wide coverage at 70 km spacing - Sufficient
    Density to allow network corrections
  • Real-Time corrections made available to
    Geo-Spatial Community
  • Improved GPS Elevations

34
  • Phase I
  • Evaluate Hardware, Software, installation methods
  • Install 4 stations in urban areas.
  • Install 1 station in vicinity of tide gauge at
    Dauphin Island
  • Provide real-time, single base-line solutions via
    internet
  • Phase II
  • Add 6 (GG) CORS stations (2 were installed in
    October)
  • Develop partnerships with County Government to
    establish Co-op CORS
  • Continue leveling efforts to establish NAVD 88
    Heights to the ARP
  • Phase III - VI
  • Continue to add 4 to 6 stations a year
  • Develop partnerships with County Government to
    establish CO-OP CORS and build redundancy in the
    system.
  • Implement network solutions when sufficient
    density is reached.

35
NGS CORS Guidelines
  • GOALS
  • Improve quality of CORS data
  • Focus attention on CORS meta-data requirements
    more detailed Site Logs and Photos

Selected Items Team established to evaluate
new sites more rigorously before
including them into the CORS network
Encourage more stable sites Avoid
multipath-prone sites Radomes not
recommended except Track all satellites
regardless of their health status Track
satellites to lower elevation angles Provide
suite of photos for each site
36
Challenges of Implementing CORS
  • Site selection
  • - Must be a stable site with no obstructions
    above 5 degrees
  • - Must be within 30 meters of adequate network
    and power connections
  • - Long term survivability trees will grow and
    possibly obstruct antenna. Possible building
    additions/renovations must be considered.

37
Grangeville Idaho
Michigan DOT Towers
Tower Design
38
Challenges of Implementing CORS
  • Monument Design
  • - The ideal monument requires a large clear
    area with no possibility of future obstructions.
  • - Easy to establish NAVD 88 Elevation at ARP
  • - Roof-top mounts have proven to be very stable
    and get the antenna above most obstructions.
  • - Can be difficult to establish NAVD 88
    Elevation to the roof.
  • - The Louisiana network utilizes roof mounts.
    One site was lost during Hurricane Katrina

39
Tuscaloosa AL50
40
Birmingham AL30Roof mount at 3rd Division
Troy AL70Roof mount at 7th
Division Office
Tuscumbia AL20Roof mount at 2nd
Division Office
Montgomery AL60Roof mount at 6th
Division Office
41
Not picturedHuntsville GTAC Roof MountAuburn
ALAU Roof Mount
Mobile AL90 - ProposedRoof mount at East
Tunnel Office
Dauphin Island ALDI Roof
mount at Sea Lab
Alexander City AL40Roof mount at
4th Division Office
42
Choke Ring vs. Geodetic Antenna
  • Choke ring has typically been thought of as a
    more robust antenna.
  • Recent evaluation of the GPS data at several
    sites has shown that the Radome can cause errors
    in the position if not properly calibrated.
  • New Geodetic-quality Antenna shows near choke
    ring quality Time will tell.

43
Challenges of Implementing CORS
  • Data Communication
  • Reliable data connection to provide raw RINEX
    files from the receiver to the NGS FTP site for
    static processing as a minimum.
  • Ideally we need to provide an adequate data
    connection to send raw data from antenna to main
    server in Montgomery, calculate corrections, and
    sent back out to the internet fast enough to be
    used for real time corrections in the field.

44
Data transmission methods back to the Rover
  • Pac-Crest Radio
  • 35 watt high wattage, high heat.
  • Requires FCC License.
  • Typically a four mile radius based on terrain.
  • Higher cost per unit up front, but lower long
    term costs.
  • Possibly get the antenna higher to provide larger
    coverage area?
  • Cell modem
  • Low front end cost for equipment
  • Monthly cell bills for unlimited minutes add up.
  • Poor and spotty coverage in rural areas.
  • Wait for coverage to catch up?
  • 900 MHZ
  • Lower wattage less heat
  • Requires line of sight to repeaters and rovers
  • Other?
  • High Frequency band-width with high wattage
    transmitter (and high cost)? More difficult to
    obtain FCC licensing.
  • WI-MAX?

45
User Issues
  • Each user will have to evaluate the areas where
    the majority of their work will be performed to
    determine which cell provider gives the best
    coverage.
  • Each user will have to evaluate existing
    equipment to determine upgrades necessary to
    communicate with CORS Server.
  • Vendors are eager to work with surveyors to
    upgrade existing equipment or sell new equipment.

46
Louisiana
  • System of benchmarks has been deemed unreliable
  • Transfer NAVD 88 orthometric heights to CORS ARP
  • Allow CORS network to serve as the vertical
    control for areas of subsidence
  • Extent of subsidence into Alabama is unknown at
    this time. Project is being planned to determine
    the extent of the subsidence along the Gulf Coast.

47
Tidal Gauges Dauphin Island
  • NOAA Temporary Gauge

1968 NOAA Gauge
USACE Gauge
- Tide Gauges are tied to the Tidal Benchmarks.
Each site has several marks in close proximity to
the gauge. - Establish First or Second Order NAVD
88 Height at the Tidal Benchmark to provide an
accurate tie to Tidal Datum. - Establish NAVD 88
Height at the CORS ARP
Tidal Benchmark
48
Dauphin Island CORS Site
  • Finding a suitable site
  • Limited access to structures with suitable
    horizon and stability.
  • Providing adequate power and data communication.
  • Design and build a mount to reasonably withstand
    weather and corrosion.
  • Close proximity to Tidal Benchmarks and First
    Order NAVD 88 Benchmarks.

49
Dauphin Island CORS Site Data and Power
considerations
  • Computer Network at Sea Lab is not reliable in
    good weather.
  • - Look at the possibility of using cell modem to
    transmit the data back to the server?
  • - perform on-site testing with the equipment to
    ensure there is sufficient cell coverage and data
    transmission speed.
  • Power is susceptible to bad weather.
  • - Provide battery back up to cover power
    outages.
  • - Prepare to install solar panels and batteries
    at this or any site in the event of catastrophic
    power loss.

50
Existing Level Lines
51
  • Time series at fort Morgan CORS prior to 2005
    HARN project

52
Latest Velocity rates from Fort Morgan CORS after
2005 HARN Project
53
Southeast CORS Network May 2005
54
  • Alabama CORS October, 2006

55
(No Transcript)
56
Benefits of a CORS Network
  • Data files archived for post-processing of static
    GPS work Survey and Engineering Control Work
  • Real-Time corrections supplied to collectors of
    geo-spatial data GIS systems
  • Precision Agriculture machine guide
  • Construction machine guide
  • Emergency response
  • Navigation
  • Air-Borne GPS
  • Monitor possible crustal motion throughout the
    State
  • Eliminates need for Base Station at remote
    locations
  • Reduced equipment costs
  • Consistent positions
  • Future vertical control network
  • Satisfy most positioning needs that require
    centimeter level accuracy!

57
Aerial Mapping, photography, and Digital Terrain
Models
  • Good horizontal and vertical control is REQUIRED
    to obtain ACCURATE Digital Ortho Photographs and
    Digital Terrain Models

58
Basis or Foundation for an ACCURATE GIS
59
LAND SURVEYING
60
SAFETY / FLOODING
  • Coastal Erosion
  • Flood Stage Predictions
  • and Measurements

61
  • Remote Sensed Imagery
  • Instrumented Farm Implements
  • Crop yield monitoring equipment
  • Light Bar and Auto-Steer guidance systems
  • Results in increased crop yields, reduced
    production costs, and reduced runoff of
    fertilizer and topsoil

62
HIGHWAYS / TRANSPORTATION
  • Better Decision making for Route Location,
    Roadway Maintenance and Improvements

63
Uses of CORS Data
  • Static Post Processed using OPUS or Vendors
    software
  • Real-Time corrections transmitted directly to the
    rover in the field.

64
Static GPS
  • Raw data is collected at the receiver for two
    hours or more observing two sessions on each mark
  • Data from CORS sites are downloaded and
    post-processed with the vendors software

65
Static GPS using OPUS
  • Raw data is collected at the receiver for no less
    than one hour OPUS still prefers two hours of
    data.
  • Raw data is sent to On-line Positioning User
    Service OPUS.
  • Solution is emailed back to the user usually in
    less than five minutes.
  • Option has recently been added for the user to
    select the base stations to use for the
    processing.
  • NGS is working on routines that will process
    fast-static sessions and single frequency
    sessions.
  • There are also plans for an OPUS database that
    would contain all of the OPUS solutions. This
    data would be retrievable in much the same way a
    conventional data sheet is retrieved.
  • NGS is working towards supporting all available
    satellite signals.

66
OPUS On line Positional User Service
67
(No Transcript)
68
(No Transcript)
69
(No Transcript)
70
(No Transcript)
71
(No Transcript)
72
(No Transcript)
73
How Does OPUS Compute Position?
3 separate baselines computed 3 separate
positions averaged
74
Looking Forward
  • NGS is Developing OPUS-RS (rapid static) that
    will enable users to obtain positional
    coordinates with cm-level accuracy using only 15
    minutes of GPS carrier phase data.
  • NGS is developing OPUS-DB (OPUS DataBase) which
    will allow users to submit GPS data files,
    observation log, photos, and description. These
    marks will be made available much the same way a
    datasheet is obtained via internet.
  • NGS is exploring the use of NTRIP to stream GPS
    data from selected CORS via the Internet.
  • Equipment manufacturers have released new
    receivers capable of receiving GLONASS, Galileo,
    L2C, and L5.

75
CORS 96 vs. NAD 83/92
  • Comparisons of OPUS positions against published
    positions led ALDOT to believe that there is up
    to a 5 cm shift between the CORS 96 and 83/92.
  • Prior to the HARN observation, NGS stated that
    the 07 adjustment would adjust the 83/92 Datum,
    which are the positions currently in the
    database, to the CORS Datum.
  • The processing for the HARN Observation indicate
    that all of the existing A and B order marks
    observed fell within the Network Accuracy limits
    of 5 cm, therefore, no adjustments were made to
    the existing A and B order positions.
  • The CORS positions and the existing A and B order
    positions were held as fixed for the HARN project.

76
2003
77
2006
78
(No Transcript)
79
(No Transcript)
80
Problems
  • New A Order positions have been posted to the NGS
    database.
  • - 32-6 in Greene County shifted by 2 decimeters
    (0.66 feet).
  • - The azimuth to back-sight mate changed by
    0-00-50!
  • - 2007 Adjustment should correct this?
  • - Use the back sight mates to the new A order
    stations with caution!

81
Disclaimers
  • ALDOT does not guarantee ANY position computed
    from the CORS sites! It is the surveyors
    responsibility to ensure all field and office
    procedures have been followed to ensure the data
    is correct.
  • NGS will establish the position of the CORS and
    it will be checked daily.
  • Tuscumbia, Tuscaloosa, Troy, and Birmingham are
    running now with temporary positions established
    by the vendor. NGS will provide positions after
    inclusion into the National CORS program.
  • It is the surveyors responsibility to verify any
    position computed or calculated with any CORS
    station.
  • Repeat Observations the best way to verify a
    position is to repeat the session under a
    different satellite constellation a minimum of
    four hours separation between the end of the
    first session and the beginning of the repeat
    session.
  • To obtain 2 cm vertical, see NOS NGS 58 59.

82
Disclaimers
  • ALDOTs first priority is the collection of data
    to meet the requirements for the National CORS
    program.
  • ALDOT will attempt to maintain a continuous,
    un-interrupted flow of data, BUT we cannot
    guarantee it.
  • A web site will be established that will report
    the condition of the sites and a schedule of
    proposed maintenance or down time to the site. A
    link will be provided on the ASPLS web page to
    this site as soon as its available.

83
CORS Sites
  • Existing Public Sites
  • GTAC Huntsville Space and Rocket Center
  • ALAU City of Auburn
  • ALDOT Sites to be posted as National CORS by
    November 06.
  • AL20 Tuscumbia Second Division Office.
  • AL30 Birmingham Third Division Office.
  • AL50 Tuscaloosa Fifth Division Office.
  • AL70 Troy Seventh Division Office.
  • ALDOT Sites under construction awaiting
    approval from NGS.
  • ALDI Dauphin Island Operational by November,
    2006.
  • AL60 Montgomery Operational on October 6, 2006.
  • AL40 Alexander City Operational on October 12,
    2006.
  • Proposed Sites
  • AL90 Mobile East Tunnel Office Begin install on
    October 23, 2006.
  • AL12 Gadsden Begin install on October 30, 2006.
  • AL52 Chilton County no install date determined
    at this time.

84
  • We are requesting that each user register with
    us to obtain IP address and port numbers so that
    we can build a contact list of active users.
  • Notification of proposed work or downtime at the
    sites.
  • Notification of any changes to the system that
    may affect use.
  • Notification of new sites.
  • Attempt to get an idea about the number of users
    for future justification of funds.
  • Establish contact lists for forums, educational
    opportunities, or input from the surveying
    community.

85
Requested Information
  • Send an email to russellj_at_dot.state.al.us. In
    the email message, please provide the following.
  • Name, address, phone number
  • Type equipment (GPS, GLONASS)
  • How will you use the system Static? RTK?
  • Number of users
  • List of areas you typically work in.

86
Questions?
87
Project Control on Location Surveys
88
Location Section
  • GPS used to establish horizontal control set at
    one to two mile interval along project corridor.
  • Conventional Traverse between GPS pairs to
    establish control at approximately 1000
    intervals.
  • Conventional leveling from First or Second Order
    benchmarks through GPS and traverse marks to
    bring vertical control into the project.

89
Benefits
  • Solid foundation of horizontal and vertical marks
    to support the project from corridor study
    through construction.
  • Ability to utilize mapping, photography, and GIS
    data from any source as long as it is in a known
    datum.
  • Eliminated physical ties between projects.
  • Eliminate Coordinate Equations
  • If project control is destroyed in any phase of
    work it can easily be restored. Control points
    are never Lost.

90
Establishing Project Control
  • Search database for horizontal and vertical marks
    in the area.

91
  • Datasheet shows the mark name, lat/long,
    horizontal/vertical order designations

92
  • Latest NGS Datasheets show coordinates in meters
    in the appropriate zone
  • Recently began showing Combined Scale Factors
  • This area has a ratio of 1 part in 20,000 grid
    vs. ground distances.

93
  • Datasheet shows the type monument, stamping,
    satellite visibility, and recovery history.

94
  • Datasheet shows recovery history from initial
    monumentation to the latest recovery notes.

95
(No Transcript)
96
(No Transcript)
97
(No Transcript)
98
Static GPS Observations
  • 18 Rebar w/ cap stamped with point number and
    year set
  • Set in an area with a good horizon for satellite
    visibility
  • Set 4 to 6 underground to avoid damage by
    mowers and other hazards

99
Numbering Schemes
  • 1 County number with letter designation for
    marks established with GPS.
  • 2 Project specific point number with year for
    marks established with total station.

100
Description Writing
  • New mark is worthless unless properly described
  • Odometer log with ties to mile posts
  • Measurements to obvious objects around each point

101
GPS Observations
  • Leica 1200 Survey Grade Receivers
  • 1 hour 15 min sessions
  • Observation logs
  • Each new mark is occupied twice
  • Side ties are occupied three times
  • Enough over-kill to avoid any return trips or
    errors.

102
Leveling
  • Once marks are set Crew splits up and three men
    begin leveling while the other make the
    observations.
  • Every new mark is leveled through
  • Leica DNA 03 First Order level
  • Third Order Elevations established on each mark
  • Begin and end on Second Order, Class II Benchmark
    or better

103
Traverse
  • After GPS observations are complete, remaining
    crew members begin conventional traverse through
    project.
  • Marks are set at 1200 intervals
  • Leica TCA 2003 0.5 electronic theodolite with
    a 1mm 1ppm distance meter
  • Servo driven with Automatic Target Recognition
  • Angle is turned five times
  • Distance is taken five times each direction for a
    total of 10 distances per leg

104
Computation
  • Azimuths from GPS positions are used for
    beginning and ending azimuths
  • Software means horizontal and vertical angles
  • Distances are meaned manually (software will not
    currently do this)
  • Traverse is computed using an old Geodimeter
    program which computes azimuth closure and closes
    the angles before giving error of closure
  • Calculates Combined Scale Factor for each leg of
    the traverse and reduces the horizontal ground
    distance to a grid distance.

105
(No Transcript)
106
(No Transcript)
107
Fast Static GPS Observations
  • Not part of a control survey
  • Post-processed and computed in the same way
    static observations are processed
  • Used for DTM Topo Survey
  • Two base stations on known marks collecting data
  • Rovers collect 10 to 15 minutes of data based on
    satellite geometry

108
Real-Time GPS Observations
  • Not part of a control survey
  • Provides position and elevation as soon as the
    point is recorded
  • Used for DTM or Topo operations
  • Generates ASCII file
  • For best solution, a Site Calibration should be
    performed ?

109
Real-Time Data Collection
  • Rover collects data independently of base
  • CORS will replace the base and the cell modem
    will replace the 35 watt radio link.

110
Site Calibration
  • Base Station is set on Project Control with good
    horizon
  • Using the rover, collect 3 minutes of data on
    each project control with suitable horizon
  • Coordinates for each point are entered into
    collector
  • Collect data on points within and around the
    project

111
Site Calibration
  • After data is collected, software will produce a
    list of the points with the RMSE for each point
  • Points with larger RMSE may be removed
  • Be careful not to remove the endpoints and that
    you are not relying on midpoints within the
    project
  • Software will calculate a coordinate system for
    the project, name it, and store the system
  • Coordinate system can be transferred between
    receivers

112
Site Calibration
  • Time consuming work at the beginning of the
    project to establish localization to the project
  • Most accurate and reliable method to use
    real-time
  • Performed once on each project
  • Calibration files are stored and saved for future
    work

113
Real Time GPS Observations
  • Horizontal and Vertical Accuracy limits can be
    pre-set
  • Normally use 0.05 ft for hard surfaces and 0.1 ft
    for ground shots
  • Each rover can work independent of everything
    except the radio or cell link
  • Does not require line of sight or communication
    with instrument man
  • Does not go under tree canopy very well.

114
P4
P1
P2
P5
P3
P6
115
P4
P1
P2
P5
B9999-1
B9999-2
P3
P6
116
Issue to be Resolved
  • Is Accuracy of single base-line RTK solution
    comparable to Site Calibration?
  • Users must evaluate the data and results.

117
Questions?
Write a Comment
User Comments (0)
About PowerShow.com