1. GNSS DERIVED HEIGHTS- PART 2 NOS/NGS - 59
NGS WEBINAR – OCTOBER 7, 2009
Bill Henning
Senior Geodesist, PLS.
x 111,

2. DAY 1 GNSS DERIVED HEIGHTS DAY 2
NOS/NGS-59- Baltimore County and Fairfax County
REAL TIME HT ISSUES
DAY 1
HT MOD
GNSS HT METHODS
NOS/NGS-58

3.
“NGS 58”
“NGS 59”

4. GEOID03 is a refined model of the geoid in the United States, which supersedes the previous models GEOID90, GEOID93, GEOID96, and GEOID99. For the conterminous United States (CONUS), GEOID03 heights range from a low of –50.97 meters (magenta) in the Atlantic Ocean to a high of 2.23 meters (red) in the Labrador Strait. However, these geoid heights are only reliable within CONUS due to the limited extents of the data used to compute it.

5. ELLIPSOID, GEOID & ORTHO HEIGHTS “h = H + N”
Earth’s
Surface P
Ellipsoid
Plumb Line h Q N
Mean
Sea
Level
“Geoid”
Relationship of the mathematical ellipsoid surface with the previously developed diagram of level surfaces and orthometric heights.
There is no relationship between the ellipsoid and the gravity field. It has nothing to do with level surfaces and its surface cuts through all level surfaces; not parallel.
GPS heights are not related with the geoid - no relation to gravity field; required model to obtain differences between the geoid and ellipsoid to determine orthometric height. Ellipsoid is above the geoid in the U.S. - why its drawn this way; geoid always negative.
Geoid height (separation, undulation) - difference between the geoid and ellipsoid at any given point on the earth’s surface. H = orthometric height, h = ellipsoid height, and N = geoid height.
h=H+N - accurate to mm as long as all the components are known. PO
Ocean
h (Ellipsoid Height) = Distance along ellipsoid normal (Q to P)
N (Geoid Height) = Distance along ellipsoid normal (Q to PO)
H (Orthometric Height) = Distance along plumb line (PO to P)

6. Expected Height Accuracies
GPS-Derived Ellipsoid Heights
2 centimeters (following NOS NGS-58 Guidelines)
Geoid Heights (GEOID03)
Relative differences typically less than 1 cm in 10 km
2.4 cm RMS about the mean nationally
0.5 cm error in 10 Km
Leveling-Derived Heights
Less than 1 cm in 10 km for third-order leveling
Following developed guidelines, NOS NGS-58, produce ellipsoid heights to 2 cm.
Latest geoid model produces relative differences typically less than 1 cm in 10 km.
Inherent error sources in running levels produces 1 cm uncertainty in 10 km for Third Order leveling.

7. www.ngs.noaa.gov Available “On-Line” at the NGS Web Site:
SEARCH: “NGS 58”
Guidelines - will eventually become routine; not so much explanation of why its done but provides background information. Repeat baselines, station spacing, fixed height antenna setups, identify and control all error sources, tie local networks together, etc..
NOS NGS-58 GPS-Derived Ellipsoid Heights Guidelines will lay the foundation for GPS-Derived Orthometric Heights Guidelines. Produce 2 cm ellipsoid heights to be able to obtain 2 cm orthometric heights.

8. What has been accomplished using NGS 58?
Control recovery, campaign planning/logistics
Obs schedulules, equipment checks
Observations: Repeat base lines
Different days
Different times of day (“15 hours, 27 hours”)
(Detect, remove, reduce effects due to multipath and using the same satellite geometry)
Recommendations - no low RMS; short data sets using a small piece of satellite visibility can cause high RMS; delete suspect satellites and reprocess - can’t fix integers - something’s wrong.
Single frequency receivers will work - fix integers - short baselines - longer data sets.
Different days - schedule 2nd observation on different day if reasonable. It’s just a matter of scheduling.

9. FAIRFAX COUNTY HEIGHT MODERNIZATION PROJECT 2004-2006

10. Vector Processing Accomplished
Elevation Mask degrees
Ephemeris - Precise (typ. 14 days latency)
Tropospheric Correction Model
Iono Corrections - All baselines longer than 5 km.
Fix Integers Baselines less than 5 km: L1 fixed solution Baselines greater than 5 km: Iono free (L3) solution
Baselines must have RMS values ≤ 1.5 cm
Baselines must have difference in “up” ellipsoid height ≤ 2.0 cm
10 degree mask for data collection allows the receiver to “cleanly” lock on to low elevation satellites providing strong, continuous satellite lock when processing at 15 degrees.
Precise orbits - maybe not much different compared to broadcast orbits but could be great - IGS orbits – ITRF97 positions, ±5 cm; combination of orbits from various sources - NGS is one supplier typically with a 13 day delay; use of “rapid orbits” maybe ok; available 1 day delay for special purposes.
Ionospheric effects - can produce major height problems; eliminate, reduce, identify errors; LI/L2 differences - Iono free solution, combined L3 - removes effects caused by ionosphere. Most other errors created by ionospheric conditions are taken out in processing software. Ionospheric models work about the same above 15E; below 15 E is where the models differ.
Standard tropo models; available in software. Wet troposphere - difficult to model out; how wet is wet? Nice weather; good results - bad weather; not so good results; 2-5 cm uncertainty; also affects multipath. Dry troposphere - can be modeled fairly well; required for long lines, different conditions, large height changes over short baselines. Can change heights by 3 to 7 cm through modeling.
Recommend low RMS values, i.e., < 1.5 cm; short data sets using a small piece of satellite visibility can cause high RMS; delete suspect satellites and reprocess – if you can’t fix integers - something’s wrong.

11. Repeat Vector Analysis After Re-Processing
From To Session dh Diff Dist RMS Solution Station Station Meters cm Meters Type
BM KU G L1 fixed double
077G L1 fixed double
078R* L1 fixed double
ZINC PT A L1 fixed double
077A L1 fixed double
076A L1 fixed double
TIDE KU G L1 fixed double
077R* L1 fixed double
076R* L1 fixed double
PT TIDE A L1 fixed double
078R* L1 fixed double
076R* L1 fixed double
04KU G Iono free fixed
077G Iono free fixed
076G Iono free fixed
ZINC A Iono free fixed
077A Iono free fixed
076A Iono free fixed
Differences in GPS-derived height (dU) values between repeat baselines.
BR13 to BR14 – float solution; RMS value is low but unable to fix integers. Try to reprocess or re-observe this baseline. Note that the second and third baseline comparison is very close.
BR14 to GR15 – high RMS on all three baselines; obstructions, multipath?
BR19 to CL20 – high RMS on all three baselines. Note the second and third baselines are much closer together.
Reprocess all baselines that have repeat differences greater than 2 cm.
*NOTE - Reprocessed vectors which had differences greater than 2 cm.

12. Adjustment Procedures to Obtain
GPS-Derived NAVD’88
Orthometric Heights

13. Least Squares Adjustments
The adjustment minimizes the effects of random errors
A least squares adjustment computes a single network solution, even with redundant vectors
Least squares will highlight blunders and large errors
It will provide estimates on the precision of the coordinates for the stations

14. GPS ELLIPSOID HEIGHT HIERARCHY
HARN/Control Stations
(75 km)
Primary Base
(40 km)
Secondary Base
(15 km)
Local Network Stations
(7 to 10 km)
Appendix B.
Guidelines guarantee proper ties and provide acceptable relative accuracies.
HARN not better than 5 cm vertical accuracy absolute.
CORS getting down to 3 cm vertical accuracy absolute.
Basic concepts - nutshell overview - if errors are not large they’re probably not visible; requires redundancy and a network. 5 cm accuracy - ties to the net at least to 5 cm (network) and internally to 2 cm (local).
Layering of control to produce local network stations. Shorter baseline lengths, shorter observation times.

15. Project Adjustment Following Guidelines
CORS
HARN
NAVD’88 BM
New Station
121°40’W
122°35’W
37°50’N
38°20’N
LATITUDE
LONGITUDE
Spacing Station
Primary Base Station
8.2km

16. Adjustment of Primary Network Stations From Control
Horizontal Adjustment
(Latitude, Longitude, Ellipsoid Heights)
Minimum Constrained [One fixed station]
Fix latitude, longitude and ellipsoid height at one station
Resolve all blunders and large residuals
Determine which Control and known Primary Base Station coordinates should be fixed
Constrained [All suitable stations fixed]
Fix latitude, longitude, and ellipsoid heights at Control and known Primary Base Stations
Make sure the constraints did not distort the project
NOTE - Geoid model NOT applied at this time

17. FAIRFAX COUNTY CONTROL & PRIMARY STATIONS

18. Adjustment of Primary Base Stations
CORS
HARN
NAVD’88 BM
New Station
D191
10CC
19.0km
Primary Base Station
28.7km
25.7km
LATITUDE
38.3km
31.6km
38.7km
25.8km
LAKE
29.6km
MART
MOLA
37°50’N
122°35’W
LONGITUDE
121°40’W
Constrained Horizontally
CORS, Control Points (known Primary Control) horizontal
latitude, longitude, and ellipsoid heights
No NAVD88 orthometric heights constrained at this time

19. Adjustment of Local Network Stations
Horizontal Adjustment
(Latitude, Longitude, Ellipsoid Heights)
Minimum Constrained [One fixed station]
Fix latitude, longitude and ellipsoid height at one station
Resolve all blunders and large residuals
Evaluate coordinates at Control and Primary Base Station
should not be greatly affected by Local Station baselines
Constrained [All suitable stations fixed]
Fix latitude, longitude, and ellipsoid heights at Control and Primary Base Stations
Make sure the constraints did not distort the project
NOTE - Geoid model NOT applied at this time

20. Adjustment of Local Network Stations
CORS
HARN
NAVD’88 BM
New Station
Spacing Station
38°16’N
Primary Base Station
LATITUDE
8.2km
37°55’N
122°20’W
LONGITUDE
121°40’W
Constrained Horizontally
Existing and newly derived Primary Control horizontal
latitude, longitude, and ellipsoid heights
No NAVD88 orthometric heights constrained at this time

21. Combined Network Horizontal Adjustment
Perform combined adjustment
Control and Primary Base network along with local network
Latitude, longitude, and ellipsoid height
Use GEOID model to obtain geoid heights
Make sure combined adjustment did not distort the project

22. Combined Horizontal Adjustment
CORS
HARN
NAVD’88 BM
New Station
121°40’W
122°35’W
37°50’N
38°20’N
LATITUDE
LONGITUDE
Spacing Station
Primary Base Station
8.2km
Constrained Horizontally
CORS, Control Points and existing and new Primary Control horizontal
latitude, longitude, and ellipsoid heights
No NAVD88 orthometric heights constrained at this time

23. FAIRFAX HORIZONTAL

24. BASELINE ADJUSTMENT SUMMARY

25. Repeat Vector Analysis
From To Session dh Diff Dist RMS Solution Station Station Meters cm Meters Type
BM KU G * L1 float double
077G L1 fixed double
076G L1 fixed double
ZINC PT A L1 fixed double
077A L1 fixed double
076A L1 fixed double
TIDE KU G L1 fixed double
077G * L1 fixed double
076G * L1 fixed double
PT TIDE A * L1 fixed double
077A L1 fixed double
076A * L1 fixed double
04KU G Iono free fixed
077G Iono free fixed
076G Iono free fixed
ZINC A Iono free fixed
077A Iono free fixed
076A Iono free fixed
Differences in GPS-derived height (dU) values between repeat baselines.
BR13 to BR14 – float solution; RMS value is low but unable to fix integers. Try to reprocess or re-observe this baseline. Note that the second and third baseline comparison is very close.
BR14 to GR15 – high RMS on all three baselines; obstructions, multipath?
BR19 to CL20 – high RMS on all three baselines. Note the second and third baselines are much closer together.
Reprocess all baselines that have repeat differences greater than 2 cm.
*NOTE - Reprocess all vectors which have difference greater than 2 cm.

26. Guidelines for Establishing GPS-Derived Orthometric
Heights
(Standards: 2 cm and 5 cm)
SEARCH: “NGS 59”
Guidelines - will eventually become routine; not so much explanation of why its done but provides background information. Repeat baselines, station spacing, fixed height antenna setups, identify and control all error sources, tie local networks together, etc..
GPS-Derived Orthometric Heights Guidelines will build from the NOS NGS-58 GPS-Derived Ellipsoid Heights Guidelines. Similar format, many similar appendices, etc.

27. A Guide for Establishing GPS-Derived Orthometric Heights (Standards: 2 cm and 5 cm)
3-4-5 System
Three Basic Rules
Four Basic Control Requirements
Five Basic Procedures
General idea of guidelines.

28. Three Basic Rules Rule 1: Rule 2: Rule 3:
Follow NGS’ guidelines for establishing GPS-derived ellipsoid heights (NGS 58:Standards: 2 cm and 5 cm)
Rule 2:
Use latest National Geoid Model, i.e., GEOID09
Rule 3:
Use latest National Vertical Datum, i.e., NAVD 88
Pretty straight forward.

29. FOUR BASIC CONTROL REQUIREMENTS
BCR-1: Occupy stations with known NAVD 88 orthometric heights
Stations should be evenly distributed throughout project
BCR-2: Project areas less than 20 km on a side, surround project with NAVD 88 bench marks
i.e., minimum number of stations is four; one in each corner of project
BCR-3: Project areas greater than 20 km on a side, keep distances between GPS-occupied NAVD 88 bench marks to less than 20 km
BCR-4: Projects located in mountainous regions, occupy bench marks at base and summit of mountains, even if distance is less than 20 km
This same information is required by the GPS-derived Orthometric heights guidelines. Producing ellipsoid heights at the 2 cm level of accuracy is essential to producing accurate GPS-derived orthometric heights.
Surrounding project areas will be difficult in many instances with existing NAVD88 bench marks. Level ties may be necessary to provide this requirement.
Extra bench marks allow independent analysis through the adjustment process and may help identify potential bench marks with questionable stability or poor published elevations.
Bench marks at base and top of mountains may help identify/rectify issues that are not otherwise apparent in the geoid model.

30. BCR Example BCR1: Sketch indicates that the 20 km rule was met.
Sample GPS-derived orthometric height project illustrating conditions of basic control requirements.
NAVD88 bench marks shown as yellow boxes. Project area is larger than 20 km so minimum 20 km spacing between bench marks is required. Bench marks are scattered throughout and surround project area.
Circled bench marks are required to satisfy guidelines. Additional bench marks provide redundancy, allow checks on adjusted elevations, and could be alternate marks if one or more of the circled mark’s published elevations don’t fit the survey.
BCR2: This requirement is not applicable because the project is greater than 20 km on a side.
BCR3: Circled bench marks are mandatory. Analysis must indicate bench marks have valid
NAVD 88 heights. Other BMs can be substituted but user must adhere to 20 km requirement.
BCR4: This requirement is not applicable because project is not in a mountainous region.

31. FAIRFAX COUNTY VERTICALS USED
40 KM

32. Five Basic Procedures
BP-1: Perform 3-D minimum-constraint least squares adjustment of GPS survey project
Constrain 1 latitude, 1 longitude, 1 orthometric height (Recall that ellipsoid heights have already been analyzed and adjusted)
BP-2: Analyze adjustment results from BP-1
Detect and remove all data outliers
The basic procedures describe the network adjustment and analysis routine. You are starting with good GPS-derived ellipsoid heights. If you don’t achieve 2 cm ellipsoid heights you can’t expect 2 cm orthometric heights.
Constraining one orthometric height shifts the adjusted elevations from ellipsoid height plus geoid height to the orthometric “plane.” This provides a chance to compare the adjusted GPS-derived orthometric heights with their published orthometric elevations.

33. Plot of free adjustment ellipsoid height residuals by baseline length.
Identify and investigate residuals greater than 2 cm. Reprocess if possible, re-observe if necessary.
After performing minimum constraint adjustment, plot ellipsoid height residuals (or dU residuals) and investigate all residuals greater than 2 cm.

34. Repeat baseline comparisons also indicate which baselines will show large residuals.
Station pairs with large residuals, i.e., greater than 2.5 cm, also have large repeat base line differences. NGS guidelines for estimating GPS-derived ellipsoid heights require user to re-observe these base lines. Following NGS guidelines provides enough redundancy for adjustment process to detect outliers and apply residual on appropriate observation, i.e., the bad vector.

35. Five Basic Procedures (continued)
BP-3: Compute differences between GPS-derived orthometric heights from minimum-constraint adjustment in BP-2 and published NAVD88 orthometric heights for all known bench marks
Compare free adjusted NAVD88 elevations against published elevations. Determine trends from differences, such as slope, and which bench marks don’t fit.
Check monument type and setting information, reported station condition, and history data (i.e., mark set and leveled in 1950) to see if there is a reason for station elevation to not fit with the adjustment.

36. CONTROL COMPARISON OUTLIERS? PASSIVE CONTROL QUALITY (OVER TIME)
GEOID MODEL QUALITY

37. GPS-Derived Orthometric Heights Minus NAVD88 Heights
Geoid99
Units = Centimeters
Plot height differences on map to show trends, such as slope, and note relationship of adjacent stations. A slope or tilt across the project area is expected but large jumps between adjacent stations should not happen.
All height differences are under 5 cm and most are less than 2 cm. Almost all relative height differences between adjacent station pairs are less than 2 cm. However, most of the height differences appear to be positive relative to the southwest corner of the project.

38. Five Basic Procedures (continued)
BP-4: Determine which BMs have valid NAVD88 height values from results from BP-3
Differences need to agree 2 cm for 2 cm survey
Differences need to agree 5 cm for 5 cm survey
May detect systematic tilt over large areas
Solve for geoidal slope and scale
BP-5: Perform constrained adjustment with results from BP-4
Constrain 1 latitude, 1 longitude, all valid orthometric height values
Ensure final heights not distorted in adjustment
Constraining the selected bench marks at the 20 km spacing and comparing how the NAVD88 orthometric heights fit at the rest of the bench marks provides an excellent check on the validity of the adjusted network.
The final constrained vertical adjustment includes all orthometric heights at bench marks determined to be consistent with the rest of the network. After final constrained adjustment has been performed make sure that the constraints didn’t distort the rest of the adjustment.

39. GPS-Derived Orthometric Heights Minus NAVD88 Heights
Geoid99
Units = Centimeters
Plot height differences on map after tilted plane has been removed and note relationships especially between of adjacent stations.
The station in the far northwest corner of the project seems to be the only one that falls outside of 2 cm. This was one of the originally chosen 20 km stations. The “extra” stations allows this one to be removed as a constraint yet provide NAVD88 bench marks at the 20 km spacing.
To detect and remove any systematic trend, a tilted plane is best fit to the height differences (Vincenty 1987, Zilkoski and Hothem 1989). After a trend has been removed, all the differences are less than +/- 2 cm except for one and almost all relative differences between adjacent stations are less than 2 cm.

40. GPS-Derived Orthometric Heights Minus NAVD88 Heights
Geoid99
Units = Centimeters
Plot height differences on map after tilted plane and the one rejected NAVD88 constraint station has been removed. All remaining constrained stations show that this project is within the 2 cm standard.
The NAVD88 orthometric heights determined for the remaining stations included in this network should reflect the same differences as the constrained stations surrounding them.
After rejecting the largest height difference (-2.4 cm), of all the closely spaced station pairs only 3 are greater than 2 cm, 1 is greater than 2.5 cm and none are greater than 3 cm.

41. The red stars are the CORS used in the "Height Mod" projects.
Following NGS guidelines, achieving 2 cm or 5 cm accuracy, and submitting the project to NGS will get NAVD88 orthometric elevations published to centimeters.
Metadata will define the method of determination as that done by GPS observations using a high resolution geoid model using precise GPS observations and processing techniques.
The stations in blue designated as "Height Mod" in the NGS Integrated Database

42. Identified as Height Mod survey station
Elevation published
to centimeters
Following NGS guidelines, achieving 2 cm or 5 cm accuracy, and submitting the project to NGS will get NAVD88 orthometric elevations published to centimeters.
Metadata will define the method of determination as that done by GPS observations using a high resolution geoid model using precise GPS observations and processing techniques.
Orthometric height
determined by GPS

43. GPS-Derived Heights from GEOID03 Separation
Topography A B C D E F
Hh-N
Ellipsoid h
GEOID03 N
= Published NAVD88 Orthometric Height
= New Control

44. Constrained Vertical Adjustment
Ellipsoid Height Adjusted to Fit Constrained Orthometric Heights
GPS-Derived Orthometric Heights
Topography A B C D E F H
Geoid based on Ortho Heights
Ellipsoid h
HGPS
hadj
Adjusted
Ellipsoid N
GEOID03
GEOID03
= Published NAVD88 Orthometric Height
= New Control

45. ADJUSTMENT TO PASSIVE CONTROL

46. Combined Network Vertical Adjustment
3-D Vertical Adjustment
(Orthometric Heights)
Minimum Constrained [One fixed station]
Fix latitude, longitude, and orthometric height at one station
Resolve all blunders and large residuals
Compare orthometric heights from adjustment with published NAVD 88
Determine which NAVD 88 bench marks should be fixed
Constrained [All suitable orthometric heights fixed]
Fix latitude, longitude at one station
Fix orthometric heights at all suitable stations
Make sure the constraints did not distort the project

47. Minimally Constrained Vertical Adjustment
CORS
HARN
NAVD’88 BM
New Station
121°40’W
122°35’W
37°50’N
38°20’N
LATITUDE
LONGITUDE
Spacing Station
Primary Base Station
8.2km
Constrained Vertically
1 horizontal latitude and longitude
1 NAVD88 orthometric heights

48. Constrained Vertical Adjustment
CORS
HARN
NAVD’88 BM
New Station
121°40’W
122°35’W
37°50’N
38°20’N
LATITUDE
LONGITUDE
Spacing Station
Primary Base Station
8.2km
Constrained Vertically
1 horizontal latitude and longitude
All valid NAVD88 orthometric heights

49. Published NAVD88 to GPS Derived
NGS Data Sheet - GEOID03
Published NAVD88 to GPS Derived
H = h
- N =
69.78
- (-32.60) 
! GEOID 09
Typical published NGS data sheet with current coordinate and height information. This is one of the bench marks observed with GPS in the San Francisco Bay Demonstration Project. GPS 2 cm heights determined on a NAVD88 bench mark.
The published NAVD88 orthometric height does not equal the published ellipsoid height minus the geoid height as indicated by the equation H=h-N.
These heights were determined by two entirely different methods, GPS-derived orthometric heights (ellipsoid heights minus geoid heights) and leveling-derived orthometric heights (optical leveling plus orthometric corrections), not to mention bench mark stability, and reflects our uncertainty of each. As our understanding and models improve this disparity should become smaller, as indicated between the various geoid models, but will never really equal.
GEOID96 = 0.17 m
GEOID99 = 0.11 m
GEOID03 = 0.05 m
GEOID 09 = m

50. SUMMARY
Mistakes and systematic errors must be removed before the adjustment
A least squares adjustment handles random errors and provides a single solution (Try to eliminate all systematic errors)
The Minimally Constrained adjustment checks the internal consistency of the network
The Constrained adjustment checks the existing control and references the network to the datum
The vertical adjustment estimates GPS-derived Orthometric heights- Approaching 3rd order leveling accuracies

51. ORTHOMETRIC HEIGHTS FROM REAL TIME GNSS POSITIONING
NAD 83 ELLIPSOID + NGS HYBRID GEOID MODEL OR
LOCK TO PASSIVE MONUMENTATION (INCLINED PLANE + NGS HYBRID GEOID MODEL) OR
DIFFERENCE IN ELLIPSOID HEIGHTS FOR ≤ 10 Km

52. REAL TIME GNSS POSITIONING USERS GUIDELINES

53. >200 RTN WORLD WIDE
>80 RTN IN USA 35+ STATE DOT MANY COOP EFFORTS

54. SUMMARY TABLE FROM THE SINGLE-BASE GUIDELINES

55. BEST METHODS FROM THE GUIDELINES: THE 7 “C’S” of NOAA’s NGS
SEARCH: “CLASSICAL REAL TIME”
CHECK EQUIPMENT
COMMUNICATION
CONDITIONS
CALIBRATION (OR NOT)
COORDINATES
COLLECTION
CONFIDENCE
THE CONTROL IS AT THE POLE

56. METADATA
BESIDES ATTRIBUTE FIELDS, THE RT PRACTICIONER MUST KEEP RECORDS OF ITEMS NOT RECORDED IN THE FIELD, FOR INSTANCE:
WHAT IS THE SOURCE OF THE DATA?
WHAT IS THE DATUM/ADJUSTMENT/EPOCH?
WHAT ARE THE FIELD CONDITIONS?
WHAT EQUIPMENT WAS USED, ESPECIALLY- WHAT ANTENNA?
WHAT FIRMWARE WAS IN THE RECEIVER & COLLECTOR?
WHAT REDUNDANCY, IF ANY, WAS USED?

57. QUICK FIELD SUMMARY: Set the base at a wide open site
Set rover elevation mask between 12° & 15°
The more satellites the better
The lower the PDOP the better
The more redundancy the better
Beware multipath
Beware long initialization times
Beware antenna height blunders
Survey with “fixed” solutions only
Always check known points before, during and after new location sessions
Keep equipment adjusted for highest accuracy
Communication should be continuous while locating a point
Precision displayed in the data collector can be at the 68 percent confidence level, which is only about half the error spread to get 95 percent confidence
Have back up batteries & cables
RT doesn’t like tree canopy or tall buildings

58. THE QUICK SUMMARY BOILED DOWN:
COMMUNICATIONS: THE KEY TO SUCCESS
CHECK SHOT: FIRST BEFORE NEW WORK
REDUNDANCY: FOR CONFIDENCE

59. CONSTRAINING PASSIVE MARKS

60. CALIBRATIONS/VERTICAL LOCALIZATIONS

61. USING OPUS-S OR OPUS –RS WITH REAL TIME POSITIONING FOR SMALL PROJECTS

64. GNSS DERIVED HEIGHTS Summary of expected orthometric precisions/accuracies REMEMBER REDUNDANCY AND A CHECK ON KNOWN POINTS
CORS = 0.05 m
OPUS-S = 0.05 m
OPUS-RS = 0.05 m
NGS 58/59 = 0.02 m local, 0.05 m to NSRS
SINGLE BASE REAL TIME = m ≤ 10 Km, remember GIGO
RTN = m,