what are control monuments
there are locations whose precise horizonatal location have been established by high precision surveys
what are benchmarks in relations to benchmarks
control monuments with established precise elevations
What is NOAA
national oceanic and atmospheric administration
national geodetic survey is part of NOAA
what does national geodetic survey do
defining, managing the national coordinate systems
US federal agency
what are the north american horizontal datums
- new england datum 1879
- united states standard datum of 1901
- north american datum 1913
- north american datum 1927- NAD 27
- north american datum 1983
13, 27, 83
world horizonal datums
- WGS84- world geodetic system
- ITRF00- international terrestrial reference frames
north american datum of 1927 is a geodetic datum
uses clarke ellipsoid of 1866
what is a geodectic datum
reference ellipsoid fixed in some manner to aphysical location on the earth’s surface
what is a geocentric datum
the origin is the earth’s center of mass
nad 83 is a geocentric datum
reference geodectic reference system 1980 ellipsoid (GRS-80)
based on terrestial and satellite observations
datum meaning (geodectic)
A geodetic datum is an abstract coordinate system with a reference surface (such as sea level) that serves to provide known locations to begin surveys and create maps
Where is the orgini of NAD 27
meades ranch, osborne county, Kansas
Is the shift between NAD-27 and NAD-83 uniform across the United States?
No
There is no single value that can be applied to convert Latitude & Longi
How much can geodetic positions of control points change when converting between NAD-27 and NAD-83 in the continental United States?
10m – 100m within the continental United States
How much can geodetic positions change when converting between NAD-27 and NAD-83 in Alaska?
more than 200m
How much can geodetic positions change when converting between NAD-27 and NAD-83 in Hawaii?
more than 400m
NCAT
NGS Coordinate Conversion and Transformation Tool
What does NGVD-29 stand for?
National Geodetic Vertical Datum of 1929.
What was NGVD-29 originally known as and when was it renamed?
NGVD-29 was originally known as the “Sea Level Datum” and was renamed in 1973.
what is EDM
electronic distance measurement
what are the 3 methods of establishing control network
triangulation, transversing, trilateration
FGCS
Federal geodectic control subcomittee
