vertical control
DESCRIPTION
Vertical Control. Vertical Datums. A vertical datum is used for measuring the elevations of points on the earth's surface. Geodetic Datums (NGVD29, NAVD88) Hydrologic Datums (LWRP, IGLD) Tidal Datums (MSL or LMSL, MLLW, MHW) Local (Cario, Memphis Datum) Ellipsoid (Space-based) Surfaces. - PowerPoint PPT PresentationTRANSCRIPT
1/10
2/10
3/10
Vertical DatumsVertical Datums
A vertical datum is used for measuring the elevations of points on the earth's surface.
– Geodetic Datums (NGVD29, NAVD88) – Hydrologic Datums (LWRP, IGLD)– Tidal Datums (MSL or LMSL, MLLW, MHW)– Local (Cario, Memphis Datum) – Ellipsoid (Space-based) Surfaces
Influenced by Gravity
Not Influenced by Gravity
4/10
Orthometric HeightsComparison of Vertical Datum Elements
NGVD 29 NAVD 88
DATUM DEFINITION 26 TIDE GAUGES FATHER’S POINT/RIMOUSKI IN THE U.S. & CANADA QUEBEC, CANADA
BENCH MARKS 100,000 450,000
LEVELING (Km) 102,724 1,001,500
TIDAL EPOCH None 1960 - 1978
GEOID FITTING Distorted to Fit MSL Gauges Best Continental Model
Vertical DatumsVertical Datums
5/10
The North American Vertical Datum of 1988 is referenced to 1 tide
gage on the St. Lawrence Seaway
1,000,000+ km
The Sea Level Datum of 1929 was
referenced to 26 tide gages in the US and
Canada~100,000 km
The Sea Level Datum of 1929’s name was
changed to the National Geodetic
Vertical Datum in 1973
6/10
7/10
4 cm
125 cm
70 cm
85 cm 102 cm
NGVD 29Referenced to 26 Tide Gages
NAVD 88Referenced to 1 Tide Gage
(Father’s Point)
NAVD88 minus LMSL(1960-1978)
-23 cm
-23 cm
-11 cm
-11 cm
8/10
• NOAA's National Geodetic Survey (NGS) defines and manages a national coordinate system.
• This network, the National Spatial Reference System (NSRS), provides the foundation for our spatial infrastructure
• NGS develops Federal standards for geodetic surveys and helps to coordinate surveying methods.
• NGS State Geodetic Advisors are stationed in several states to work with local communities to expand surveying capabilities.
9/10
Changing Elevations in a Dynamic EnvironmentChanging Elevations in a Dynamic Environment
10/10
Changing Elevations in a Dynamic EnvironmentChanging Elevations in a Dynamic Environment
11/10
Additional Information Available at:
http://crunch.tec.army.mil/information/SM_CoP/ndsp