Aerospace Blockset™

LLA to ECEF Position - Calculate Earth-centered Earth-fixed (ECEF) position from geodetic latitude, longitude, and altitude above planetary ellipsoid

Library

Utilities/Axes Transformations

Description

The LLA to ECEF Position block converts geodetic latitude , longitude , and altitude above the planetary ellipsoid into a 3-by-1 vector of ECEF position . The ECEF position is calculated from geocentric latitude at mean sea-level and longitude using:

where geocentric latitude at mean sea-level and the radius at a surface point are defined by flattening , and equatorial radius in the following relationships.

Dialog Box

Units

Specifies the parameter and output units:

Units	Altitude	Equatorial Radius	Position
`Metric (MKS)`	Meters	Meters	Meters
`English`	Feet	Feet	Feet

This option is only available when Planet model is set to Earth (WGS84).

Planet model

Specifies the planet model to use: Custom or Earth (WGS84).

Flattening

Specifies the flattening of the planet. This option is only available with Planet model set to Custom.

Equatorial radius of planet

Specifies the radius of the planet at its equator. The units of the equatorial radius parameter should be the same as the units for altitude. This option is only available with Planet model set to Custom.

Inputs and Outputs

Input	Dimension Type	Description
First	2-by-1 vector	Contains the geodetic latitude and longitude, in degrees.
Second	Scalar	Contains the altitude above the planetary ellipsoid.

Output	Dimension Type	Description
First	3-by-1 vector	Contains the position in ECEF frame, in same units as altitude.

Assumptions and Limitations

The planet is assumed to be ellipsoidal by setting flattening to 0.0 a spherical planet can be achieved.

The implementation of the ECEF coordinate system assumes that the origin is at the center of the planet, the x-axis intersects the Greenwich meridian and the equator, the z-axis being the mean spin axis of the planet, positive to the north, and the y-axis completes the right-handed system.

References

Stevens, B. L., and F. L. Lewis, Aircraft Control and Simulation, John Wiley & Sons, New York, 1992.

Zipfel, P. H., Modeling and Simulation of Aerospace Vehicle Dynamics, AIAA Education Series, Reston, Virginia, 2000.

"Atmospheric and Space Flight Vehicle Coordinate Systems," ANSI/AIAA R-004-1992.