geodesy basics for kentucky gis

Ross MackayKentucky Geodetic Advisor

Geodesy Basicsfor

Kentucky GIS

2009 Kentucky Geospatial SummitFrankfort, KentuckySeptember 10, 2009

ellipsoid

Datum

geoid

Datum

• Latitude • Longitude • Height • Scale • Gravity• Orientation

National Spatial Reference SystemNSRS

Geodesy layer

and how these values change with time

Datum

h

LandSurface

h = Ellipsoidal Height

Ellipsoid

Geoid model

?

H

H = “elevation”

N = Geoid height

H ≈ h - N

Datum

N

Passive Control

TRANSCONTINENTAL ARC OF TRIANGULATION

http://www.holoscenes.com/cgi-bin/moin.cgi/TranscontinentalTriangulation

Map courtesy of Jim Irwin

KGRN (NSRS 2007) 863

Horizontal 2079

Vertical 10123

Datum

Active Control

National CORS Network

1381 National CORSSeptember 1, 2009

CORS

• Paducah, KYTA

• Jackson, KYTJ

• Morehead, KYMH

• Cumberland, KYCB

• Somerset, KYSC

• Campbellsville, KYCB

• Taylor Lake, Lou5

• Madisonville , KYTB

• Bowling Green, KYTC

• Elizabethtown, KYTD

• Louisville, KYTE

• Covington, KYTF

• Lexington, KYTG

• Somerset, KYTH

• Flemingsburg, KYTI

• Manchester, KYTK

• Pikeville, KYTL

• Greenbo Lake SRP, KYGB

• Dale Hollow SRP, KYDH

• Rough River SRP, KYRR

CORS

Hyperactive Control

NSRS

NSRS

NAD 83 vs. ITRF00

2.2 meters

NAD 83 origin

ITRF 00 origin

Earth’s

Surface

h83

h00

Identically shaped ellipsoids (GRS-80)a = 6,378,137.000 meters (semi-major axis)1/f = 298.25722210088 (flattening)

NSRS

NAVD 88Referenced to Father’s Point

NSRS

GRAV-DNGS 10-Year Plan

NSRS

Ten-Year Milestones (2018)

• NGS will redefine the NSRS vertical datum based on GNSS and a gravimetric geoid.

• NGS will redefine the NSRS horizontal datum, removing disagreement with the ITRF.

NSRS

Predicted positional changes fordatums in 2018

(Florida example)

Horizontal = 0.82 m (2.7 ft)

Ellipsoid Height

=

- 1.55 m (- 5.1 ft)

Predicted with HTDP

Orthometric Height

=

- 0.04 m (- 0.1 ft)

Predicted with HTDP and USGG2009

NSRS

Ross MackayKentucky Geodetic Advisor

ross.mackay@ky.gov

on the web atngs.ky.gov

(502) 564-1474