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The Norwegian standard for satellite based positioning

The Norwegian standard for satellite based positioning. Anders Solberg Geodetic institute, Norwegian Mapping Authority (NMA). Norwegian standards for geographic information. The standard for spatial data. Placement of buildings. Geodetic networks. Maps and spatial data.

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The Norwegian standard for satellite based positioning

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  1. The Norwegian standard for satellite based positioning Anders Solberg Geodetic institute, Norwegian Mapping Authority (NMA)

  2. Norwegian standards for geographic information The standard for spatial data Placement of buildings Geodetic networks Maps and spatial data Land property information Satellite based positioning Other standards Coordinate based reference systems

  3. Background • Work on the standard “Satellite based positioning” started in 1998 • The following institutions have been represented in the working group: • The national road administration • The municipalities • Norwegian University of Life Sciences (formerly Agricultural University of Norway) • Aerial photography companies • Norwegian Mapping Authority (Statens kartverk) • Version 1.0 released in 2000 • Minor revisions in 2001 • New methods emerging, changes in older methods  Version 2.0 (current version) released in January 2005

  4. Main contents in the standard • Overview over different GNSS positioning methods and their respective accuracy potential • General guidelines for use of GNSS • Guidelines for positioning with code ranges • Single Point Positioning (real-time) • Traditional (single base) DGPS • Network DGPS • Guidelines for positioning with carrier phase ranges • Precise Point Positioning (PPP) • Static relative positioning • Traditional (single base) RTK • Network RTK

  5. RTK guidelines include… • Survey planning • Field work • Use of one reference station • Use of more reference stations with time separation for redundancy reasons (independent baselines) • Surveying routines • (Computations), documentation and reporting

  6. Surveying routines (1) • Setup of reference station • Setup of rover • Control of the reference station setup and datum transformation parameters • Control of initialization. Possible methods: • Automatically in the rover (if such software is installed) • Measuring points with known coordinates • If more ref.stations available: Measuring using another ref.station The initialization shall be controlled every time a fixed solution is lost and a re-initialization has been made (!)

  7. Surveying routines (2) • Control of observation quality • “The number of available satellites should at least be 5 (preferably 6-7)” • “The accuracy indicators and the DOP values shall be lower than the recommended boundaries given in the receiver’s user manual”

  8. Network RTK • A short description of the VRS principle (no other NRTK techniques, as this was the only one available in Norway in 2004) • The same surveying routines as for single base RTK are valid. • Important to use “null-antenna” as reference sensor antenna model in the rover

  9. Adjustment and analysis (trad. RTK) For some applications, this may be necessary (e.g. in case of surveying of ground control points for photogrammetric use) • In this case, the standard points at the same computation procedure as used in adjustment and analysis of a network of post processed baselines: • Detection of gross errors • Testing of the points that have known coordinates (necessary in the RTK case?) • Reliability analysis • Internal reliability (how well the baselines control each other) • External reliability (effects of gross errors onto the unknown coordinates) • Final adjustment of coordinates (without baselines with gross errors) • Quality requirements are in at least two of the other standards related to the external reliability.

  10. Adjustment and analysis (NRTK) • When NRTK has been used, it might be convenient to use coordinates (N,E,h) instead of baselines (ΔN, ΔE, Δh) as input in the process. • One reason: If baselines are to be used, the surveyor has to stay connected to the NRTK service all the time when points that he wants referred to the same base point (i.e. VRS) are measured. VRS 2 VRS 1

  11. “Independent” measurements • RTK measurements are generally time correlated due to e.g. slowly varying satellite geometry • The statistical assumptions for the reliability analysis are broken down • Erroneous fixed RTK solutions may not be detected • The standard recommends these procedures to obtain “independent” measurements of the same point: Either: Two measurements separated by 45 minutes Or: Three measurements, each separated by 15 minutes

  12. Is the standard being followed??? • Yes, at least to some extent • But many users have problems with waiting 45 minutes between two measurements of the same point (time = money) • The standard is not yet part of the law on land property registration

  13. Integrity – will the standard be obsolete? • NATO’s definition: “The ability of a navigation system to provide timely warnings to determine if and when the system should not be used” • Many RTK users have to document their surveying results with respect to the reliability of the computed coordinates • EGNOS provides a “protection level” parameter , i.e. a real-time “accuracy guarantee” • Could a calculation of an adequate protection level be possible in the Network RTK case?

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