Format of the "GPS/Leveling" file 01-30 Station Name character, left justified 31-32 Geodetic Lat., deg. integer, right justified 33-34 Geodetic Lat., min. integer, right justified 35-41 Geodetic Lat., sec. integer, right justified, units 0.00001" 42-42 Code (N/S) character, upper case 43-45 Geodetic Lon., deg. integer, right justified 46-47 Geodetic Lon., min. integer, right justified 48-54 Geodetic Lon., sec. integer, right justified, units 0.00001" 55-55 Code (E/W) character, upper case 56-62 Ellipsoidal Height integer, right justified, units of 1 mm 63-63 blank 64-70 Orthometric Height integer, right justified, units of 1 mm 71-72 blank 73-76 Ortho Datum Code alphanumeric character, upper case 77-77 blank 78-79 Ellipsoid OC Code integer, right justified 80-81 State ID characters, upper case 82-87 Permanent ID (PID) six alphanumeric characters, any order 88-93 North-South accuracy real, two significant digits, cm 94-99 East-West accuracy real, two significant digits, cm 100-102 blank 103-113 correlation coefficient 114-114 blank 115-119 vertical accuracy real, two significant digits, cm 120-120 blank 121-121 reject character, either case COMMENTS Ortho Datum Code ---------------- Code Explanation H 88 North American Vertical Datum of 1988 Reject Code ----------- Rejection is based on three tests. The first test is to evaluate the given ellipsoid height errors and determine outliers. Points outside of the 95% confidence level (two sigma) after 4 iterations are rejected and assigned 'h'. Points are then compared to a gravimetric geoid to form residuals. Points with abnormally large residual values are dropped as having a bad orthometric height 'H'. Finally, points that are rejected after modeling has started due high residuals after LSC modeling are assigned a code of 'N'. h Ellipsoid height error H Orthometric height error N Geoid height error Blank Indicates no rejection. Ellipsoid Order & Class (OC) Codes ---------------------------------- The OC codes are used to classify each ellipsoid height value observed and adjusted at horizontal control points. The first character indicates order while the second indicates class in accordance with the following draft standards for classifying ellipsoid height determinations: OC Code Classification b = maximum height difference accuracy 00 NRA2007 absolute accuracy determined instead 11 First Order, Class I 0.5 12 First Order, Class II 0.7 21 Second Order, Class I 1.0 22 Second Order, Class II 1.3 31 Third Order, Class I 2.0 32 Third Order, Class II 3.0 41 Fourth Order, Class I 6.0 42 Fourth Order, Class II 15.0 51 Fifth Order, Class I 30.0 52 Fifth Order, Class II 60.0 The ellipsoid height difference accuracy (b) is computed from a minimally constrained, correctly weighted, least squares adjustment by the formula: b = s / sqrt(d) where: d = horizontal distance in kilometers between control points s = propagated standard deviation of ellipsoid height difference in millimeters between control points obtained from the least squares adjustment The following table lists the standard errors of ellipsoid height differences at various distances: Standard Error (mm) DISTANCE| OC Code (km) | 11 12 21 22 31 32 41 42 51 52 ________|_________________________________________________ 1 | 0.5 0.7 1.0 1.3 2 3 6 15 30 60 5 | 1.1 1.6 2.2 2.9 4.5 6.7 13 34 67 134 10 | 1.6 2.2 3.2 4.1 6.3 9.5 19 47 95 190 25 | 2.5 3.5 5.0 6.5 10 15 30 75 150 300 50 | 3.5 4.9 7.1 9.2 14 21 42 106 212 424 75 | 4.3 6.1 8.7 11 17 26 52 130 260 520 100 | 5.0 7.0 10 13 20 30 60 150 300 600 State ID -------- This code conforms to the standard two digit abbreviations for states in the United States. Additionally, codes of 'DC' and 'CD' are used to denote points located in the District of Columbia and the country of Canada, respectively. Permanent ID (PID) ------------------ Most NGS control points have a Permanent IDentifier (PID) associated with them. A PID for a point does not change and consists of 6 alphanumeric characters with any alpha characters being upper case. Recently acquired GPS on bench mark points used in this analysis that have not been assigned a PID were instead assigned an identifier 'DRUnnn', where nnn ranges between 002 and 152. North-South, East-West, and Vertical Accuracy ---------------------------------------------- For points in the National Readjustment of 2007, error estimates are provided for these points. All values are given in cm. the correlation coefficient represents the correlated signal between the N-S and E-W components.