What is a Geodetic Datum?
A geodetic datum is a coordinate system and set of reference points used to locate places on Earth. It provides a foundation for measuring locations, heights, and distances on our planet's surface.
Key Components
- Reference Ellipsoid: Mathematical model approximating Earth's shape
- Origin Point: Fixed reference point for measurements
- Orientation: Alignment relative to Earth's rotation axis
Common Geodetic Datums
WGS84
World Geodetic System 1984
- • Global GPS reference system
- • Earth's center of mass as origin
- • Updated regularly for precision
Semi-major axis: 6,378,137.0 m
Flattening: 1/298.257223563
Flattening: 1/298.257223563
NAD83
North American Datum 1983
- • Standard for North America
- • Compatible with WGS84
- • Multiple realizations
Semi-major axis: 6,378,137.0 m
Flattening: 1/298.257222101
Flattening: 1/298.257222101
ETRS89
European Terrestrial Reference System 1989
- • European standard datum
- • Fixed to Eurasian plate
- • High precision network
Semi-major axis: 6,378,137.0 m
Flattening: 1/298.257222101
Flattening: 1/298.257222101
Datum Transformations
Common Methods
3-Parameter (Molodensky)
- • Simple translation (ΔX, ΔY, ΔZ)
- • Suitable for small areas
- • Lower accuracy
7-Parameter (Helmert)
- • Translation + rotation + scale
- • Higher accuracy
- • Continental scale transformations
Grid-based
- • Highest accuracy
- • Regional distortion modeling
- • Complex implementation
Transformation Parameters
Translation (m)
- ΔX: -8.0
- ΔY: 160.0
- ΔZ: 176.0
Rotation (″)
- RX: 0.1507
- RY: 0.0446
- RZ: -0.0542
Scale (ppm)
0.039
Epoch
2010.0
Modern Applications
GNSS Applications
- • Precise Point Positioning (PPP)
- • Real-Time Kinematic (RTK)
- • Navigation systems
- • Asset tracking
GIS Integration
- • Spatial data management
- • Web mapping services
- • Location-based services
- • Environmental monitoring
Engineering
- • Construction layout
- • Infrastructure design
- • Deformation monitoring
- • Machine control