EndRun Tempus LX GPS, User Manual

Page: 88 / 116

T e m p u s L X G P S U s e r M a n u a l 76
A P P E N D I X D
JT9450
JT9450 NGVD 29 - 46.412 (m) 152.27 (f) ADJUSTED 1 2
JT9450
JT9450.Superseded values are not recommended for survey control.
JT9450.NGS no longer adjusts projects to the NAD 27 or NGVD 29 datums.
JT9450.See file dsdata.txt to determine how the superseded data were derived.
JT9450
JT9450_MARKER: DB = BENCH MARK DISK
JT9450_SETTING: 38 = ABUTMENT
JT9450_STAMPING: B 1397 1987
JT9450_MARK LOGO: NGS
JT9450_STABILITY: B = PROBABLY HOLD POSITION/ELEVATION WELL
JT9450
JT9450 HISTORY - Date Condition Report By
JT9450 HISTORY - 1987 MONUMENTED NGS
JT9450
JT9450 STATION DESCRIPTION
JT9450
JT9450’DESCRIBED BY NATIONAL GEODETIC SURVEY 1987
JT9450’IN SANTA ROSA.
JT9450’IN SANTA ROSA, AT THE INTERSECTION OF U.S. HIGHWAY 101 AND STATE
JT9450’HIGHWAY 12, SET VERTICALLY IN THE SOUTH FACE OF THE NORTH CONCRETE
JT9450’ABUTMENT OF THE SOUTHBOUND U.S. HIGHWAY OVERPASS OF THE STATE
JT9450’HIGHWAY, 6.7 M (22.0 FT) WEST OF THE CENTER OF THE SOUTHBOUND LANES
JT9450’OF THE U.S. HIGHWAY, 5.6 M (18.4 FT) NORTH OF THE CENTERLINE OF THE
JT9450’WESTBOUND LANES OF THE STATE HIGHWAY, AND 0.3 M (1.0 FT) EAST OF THE
JT9450’WEST END OF THE ABUTMENT.
JT9450’THE MARK IS 1.4 M ABOVE A SIDEWALK.
*** retrieval complete.
Elapsed Time = 00:00:01
The height data for this benchmark was not obtained via GPS and so does not directly contain height
above the ellipsoid, but we can obtain that information by adding the orthometric height (47.27 me-
ters) to the geoid height (-31.28 meters). In this case, the ellipsoid height of the benchmark is 15.99
meters. This benchmark is .4 miles from the EndRun Technologies facility. The GPS antenna at the
facility is located on the rooftop of a three story office building which would place it about 15 meters
above the street level. If we add 15 meters to the benchmark height we estimate the antenna height at
30.99 meters.
The GPS receiver actually reports a WGS-84 height of 32 meters, which gives remarkably close
agreement. In general, you should not expect results that are this good. Downtown Santa Rosa is
located on a very flat plain so that relatively distant survey points give acceptable results. You should
exercise some judgment in selecting particular survey points to use for your location. As an example,
if you know that the terrain west of your facility rises or falls rapidly you should avoid using bench-
marks that are west of your facility.