EndRun Tempus LX GPS, User Manual, Page: 87 / 116

T e m p u s L X G P S U s e r M a n u a l 74
A P P E N D I X D
75 T e m p u s L X G P S U s e r M a n u a l
G P S R E F E R E N C E P O S I T I O N
and make the assumption that its height is close to your street height. From the same NGS/NOAA
website, you can obtain a list of survey benchmarks that are within a user-specified radius of the
NAD-83 latitude and longitude coordinates you previously determined. Of these, some are vertical
control points, meaning that they have height data as well as latitude and longitude data. You can
select one, or several of these that are closest to your location and download the datasheets for those
benchmarks.
Some of these vertical control point datasheets are based on GPS survey measurements and contain
the height above the NAD-83 ellipsoid information. If so, then you can use that height directly along
with the NAD-83 latitude and longitude coordinates you previously determined. Other vertical
control point datasheets will give only the orthometric height, which is the height above the geoid.
Fortunately, the height of the geoid above the WGS-84 ellipsoid is also contained in the datasheet.
So, to obtain the height above the ellipsoid you must add the orthometric height and the geoid height
together. Make any adjustments to the height that might be necessary if the antenna is installed in a
high-rise building. Armed with coordinates in the NAD-83 datum, you can input them to the Tempus
LX via the
setgpsrefpos
command.
The following is a sample datasheet for a benchmark that is near the EndRun Technologies facility in
downtown Santa Rosa, CA:
DATABASE = Sybase ,PROGRAM = datasheet, VERSION = 6.57
1 National Geodetic Survey, Retrieval Date = JANUARY 23, 2002
JT9450 ***********************************************************************
JT9450 DESIGNATION - B 1397
JT9450 PID - JT9450
JT9450 STATE/COUNTY- CA/SONOMA
JT9450 USGS QUAD - SANTA ROSA (1994)
JT9450
JT9450 *CURRENT SURVEY CONTROL
JT9450 ___________________________________________________________________
JT9450* NAD 83(1986)- 38 26 44. (N) 122 43 25. (W) SCALED
JT9450* NAVD 88 - 47.270 (meters) 155.09 (feet) ADJUSTED
JT9450 ___________________________________________________________________
JT9450 GEOID HEIGHT- -31.28 (meters) GEOID99
JT9450 DYNAMIC HT - 47.241 (meters) 154.99 (feet) COMP
JT9450 MODELED GRAV- 980,011.6 (mgal) NAVD 88
JT9450
JT9450 VERT ORDER - FIRST CLASS II
JT9450
JT9450.The horizontal coordinates were scaled from a topographic map and have
JT9450.an estimated accuracy of +/- 6 seconds.
JT9450
JT9450.The orthometric height was determined by differential leveling
JT9450.and adjusted by the National Geodetic Survey in June 1991.
JT9450
JT9450.The geoid height was determined by GEOID99.
JT9450
JT9450.The dynamic height is computed by dividing the NAVD 88
JT9450.geopotential number by the normal gravity value computed on the
JT9450.Geodetic Reference System of 1980 (GRS 80) ellipsoid at 45
JT9450.degrees latitude (g = 980.6199 gals.).
JT9450
JT9450.The modeled gravity was interpolated from observed gravity values.
JT9450
JT9450; North East Units Estimated Accuracy
JT9450;SPC CA 2 - 586,710. 1,936,830. MT (+/- 180 meters Scaled)
JT9450
JT9450 SUPERSEDED SURVEY CONTROL