Format of the "GPS/Leveling" file (code: eval3 August 10, 1999 DAS) 01-04 Station Serial Number integer, right justified 05-34 Station Name character, left justified 35-36 Geodetic Lat., deg. integer, right justified 37-38 Geodetic Lat., min. integer, right justified 39-45 Geodetic Lat., sec. integer, right justified, units 0.00001" 46-46 Code (N/S) character, upper case 47-49 Geodetic Lon., deg. integer, right justified 50-51 Geodetic Lon., min. integer, right justified 52-58 Geodetic Lon., sec. integer, right justified, units 0.00001" 59-59 Code (E/W) character, upper case 60-66 Ellipsoidal Height integer, right justified, units of 1 mm 67-67 blank 68-74 Orthometric Height integer, right justified, units of 1 mm 75-75 blank 76-76 GPS Order (Hztl) character, upper case 77-77 Ortho Elevation Code character, upper case 78-78 Ortho Order character, upper case 79-79 Ortho Datum Code character, upper case 80-80 Reject Code character, upper case 81-82 Ellipsoid OC Code integer, right justified 83-84 State ID characters, upper case 85-90 Permanent ID (PID) six alphanumeric characters, any order COMMENTS Station Serial Number --------------------- Arbitrary positive index number. Not to be repeated within a given file. GPS Order (Hztl) ---------------- Code Explanation A Length Relative Accuracy (2 sigma) better than 1:10,000,000 B Length Relative Accuracy (2 sigma) better than 1: 1,000,000 1 Length Relative Accuracy (2 sigma) better than 1: 100,000 2 Length Relative Accuracy (2 sigma) better than 1: 20,000 3 Length Relative Accuracy (2 sigma) better than 1: 5,000 Ortho Elevation Code -------------------- Code Explanation A OHT established using FGCS leveling specifications and procedures, adjusted height determined using NGS Vertical Network Branch procedures, leveling data is in the NGSIDB. B OHT established using FGCS leveling specifications and procedures, adjusted height determined using NGS Vertical Network Branch procedures, leveling data is not in the NGSIDB. (USGS, COE, some state DOT data.) C OHT established using FGCS leveling specifications and procedures, adjusted height is 'posted'. See explanation in the footnote (*) below. H OHT established using FGCS leveling specifications and procedures except for the two-mark leveling tie requirement. (Horizontal field party level ties, some state DOTs, some GPS level ties.) L OHT established using leveling RESET specifications and procedures. F OHT established by fly-leveling. T OHT established by leveling between control points which are not Bench Marks. R OHT established by reciprocal vertical angles. V OHT established by non-reciprocal vertical angles. P OHT established by photogrammetry. M OHT established by scaling from a contoured map. G OHT established by GPS observations. D OHT established by datum transformations. * Data for level lines containing 'posted' BMs were purposely not included in the NAVD88 general adjustment. Subsequently, these data were adjusted to NAVD88 by forcing them to fit the existing NAVD88 general adjustment heights. Ortho Order ----------- Code Explanation 1 Relative Accuracy (2 sigma) better than 0.7 mm x sqrt(Km) 2 Relative Accuracy (2 sigma) better than 1.3 mm x sqrt(Km) 3 Relative Accuracy (2 sigma) better than 2.0 mm x sqrt(Km) Ortho Datum Code ---------------- Code Explanation blank North American Vertical Datum of 1988 9 National Geodetic Vertical Datum of 1929 Reject Code ----------- An asterisk ("*") indicates a rejection (for various experiments) 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 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.