Lecture 16 NAD 83 (1986), NAD 83(1993) and NAD 83 (NSRS 2007) 10 March 2009 GISC3325

Transcription

1 Lecture 16 NAD 83 (1986), NAD 83(1993) and NAD 83 (NSRS 2007) 10 March 2009 GISC3325

2 Significant dates March 2009 is Spring Break 12 March 2009 is Exam Two Emphasis on chapter 5, 6 and 8 of text as well as all lectures and labs. 12 March 2009 is due date for Homework 1 (see class web page). Remember to start on the Reading Assignment!

3 Assigned outside reading See class web page for links to two articles covering material to appear on the exam. NADCON VERTCON

4 Horizontal networks North American Datum of 1927 (NAD 27) In use up to 1986 Based on the Clarke Spheroid of 1866 ellipsoid. North American Datum of 1983 (NAD 83) Modified a number of times. First version NAD 83 (1986) did NOT include GPS Based on Geodetic Reference System of 1980 (GRS 80) reference ellipsoid.

5 COMPARISON OF DATUM ELEMENTS NAD 27 ELLIPSOID DATUM POINT ADJUSTMENT BEST FITTING CLARKE 1866 GRS80 a = 6,378,206.4 m 1/f = Triangulation Station MEADES RANCH, KANSAS 25k STATIONS Several Hundred Base Lines Several Hundred Astro Azimuths North America NAD 83 a = 6,378,137. M 1/f = NONE EARTH MASS CENTER 250k STATIONS Appox. 30k EDMI Base Lines 5k Astro Azimuths Doppler Point Positions VLBI Vectors World-Wide

6 BC-4 Camera Program

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9 BC-4 camera photograph stars in circular pattern satellite is a series of dots in straight line.

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11 What is to be done?

12 NGS to the rescue!

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14 NAD 83 Project Digitized observations from 1800s-1980s 300 persons, at some time in 12 years, worked on NAD 83 $37M (in 1974 dollars) 1,000,000 simultaneous equations solved using Helmert Blocking! Doppler and VLBI, but mostly terrestrial observations NAD 83 released with datum origin moved to Center Of Mass (COM) of Earth

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17 NAD 27 and NAD 83 NAD 27 and NAD 83

18 Problems with NAD 83 (1986) In 1980's GPS was adopted and as a result: Improved length determinations Observation of non-intervisible stations Ellipsoid heights now available from GPS Led to development of hybrid geoid models like GEOID To deal with these issues a state-by-state campaign of precise GPS observations was made.

19 NETWORK STATUS HPGN/HARN SURVEYS 1991 GPS341 GPS197 reos 7/96 GPS1047 GPS404 GPS GPS GPS GPS805 GPS GPS GPS633 GPS GPS GP S291 reobs 9/ GPS1150 reos-6/95-gp S904 GPS GPS725 GPS GPS908 GPS P199 S 1 GPS GPS610 GPS GPS GPS GPS G GPS882 GPS1178 os 19 GPS730 GPS re 1994 reos 1/96 GPS936 S1 70 GPS383 GPS366 GPS GPS222 -G P GPS GPS667 GPS & CLASSICAL ADJUSTMENTS COMPLETED. GPS ADJUSTMENT COMPLETED GPS577 In Texas GPS-725 original HARN and subsequent campaign to improved ellipsoid height GPS-1267 in 1998.

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21 Texas HARN GPS-725

22 HARN surveys Monument categories Federal Base Network Cooperative Base Network User Densification Network Survey accuracies GPS brought about new accuracy measures from AA, A, B, C (0.01ppm to 10 ppm respectively) State-by-state approach resulted in use of adjustment date tags e.g. NAD 83(1993) refers to the date of Texas HARN.

23 Intended policy regarding FBN in fact NOT realized.

24 Old FGCS Standards Order Base error (e) cm Line length dependent error (p) ppm Line length error as a ratio AA :100,000,000 A :10,000,000 B :1,000,000 C (1) :100,000 Accuracies shown are at 95% confidence level. Compute allowed error as sqrt(e2 + (0.1 * p * d)2 ) where d is the baseline distance in kilometers.

25 Observations At time of 1993 HARN, the requirement was for two eight-hour sessions at each site. Few GPS satellites most of the time Selective availability in effect. Primary interest in horizontal positions. In 1998 things changed...

26 FBN Reobservation Campaign With advances in GPS and recognition of the usefulness of it for height determination (ellipsoid) another state-by-state campaign was initiated. Texas project was observed as GPS

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30 Changes at Blucher Tag Lat deg min sec Lon deg min sec Difference with respect to n.a m m As seen on the preceding slide, the station was observed in only one campaign. The position changes result from the use of these observations in combination with other data and projects. Where is BLUCHER now?

31 Improving Positional Accuracy NETWORK TIME SPAN NETWORK ACCURACY LOCAL ACCURACY NAD METERS (1 part in 100,000) NAD83(86) METER HARN METER CORS meter (1 part in 100,000) B-order (1 part in 1 million) A-order (1 part in 10 million) 0.01 meter

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33 NGS CORS Status March 2009

34 NAD 83 (NSRS 2007) Project Remove inconsistencies between states Make consistent with CORS Compute Network and Local accuracies for points. September 24, 2003 NGS Executive Steering Committee approved a plan for the readjustment of the horizontal positions and ellipsoid heights for GPS stations in the contiguous United States. Orthometric Height adjustment not attempted.

35 NGS Adjustment Team NGS Adjustment Team(1986) (2005)

36 Data used in NAD 83 (NSRS 2007) Adjustment ONLY GPS DATA WAS USED CONTINUOUSLY OPERATING REFERENCE STATIONS (CORS) FEDERAL BASE NETWORK COOPERATIVE BASE NETWORK USER DENSIFICATION NETWORK AIRPORT SURVEYS

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39 Project Adjustment Analysis 3436 Projects Free Adjustment Residual Plot Outliers Rejected Connectivity to A/B Order Network Verified Summary sheet with Project Information Created stations

40 The basic stats of NSRS projects 67,693 points (203,079 unknowns) 283,691 vectors (851,073 observations) 673 CORS fixed ( m σ in 3-D) Variance of unit weight: 1.892

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43 Network Accuracy Network accuracy of a control point A value that represents the uncertainty of its coordinates with respect to the geodetic datum at the 95-percent confidence level Datum is considered to be best expressed by the Continuous Operating Reference Stations (CORS) Local and Network accuracy values at CORS sites are considered to be infinitesimal (approach zero) These accuracies will be implemented with the National Readjustment