## Documentation Center |

Convert latitude, longitude, altitude (LLA) coordinates to Earth-centered inertial (ECI) coordinates

LLA to ECI Position block converts latitude, longitude, altitude (LLA) coordinates to Earth-centered inertial (ECI) position coordinates, based on the specified reduction method and Universal Coordinated Time (UTC), for the specified time and geophysical data. Latitude and longitude values can be any value. However, latitude values of +90 and -90 may return unexpected values because of singularity at the poles.

**Reduction**Reduction method to convert the coordinates. Select one of the following:

`IAU-76/FK5`Reduce the calculation using the International Astronomical Union (IAU)-76/Fifth Fundamental Catalogue (FK5) (IAU-76/FK5) reference system. Choose this reduction method if the reference coordinate system for the conversion is FK5.

**Note:**This method uses the IAU 1976 precession model and the IAU 1980 theory of nutation to reduce the calculation. This model and theory are no longer current, but the software provides this reduction method for existing implementations. Because of the polar motion approximation that this reduction method uses, the block calculates the transformation matrix rather than the direction cosine matrix.`IAU-2000/2006`Reduce the calculation using the International Astronomical Union (IAU)-2000/2006 reference system. Choose this reduction method if the reference coordinate system for the conversion is IAU-2000. This reduction method uses the P03 precession model to reduce the calculation.

**Year**Specify the year used to calculate the Universal Coordinated Time (UTC) date. Enter a double value that is a whole number greater than 1, such as

`2013`.**Month**Specify the month used to calculate the UTC date. From the list, select the month from

`January`to`December`.**Day**Specify the day used to calculate the UTC date. From the list, select the day from

`1`to`31`.**Hour**Specify the hour used to calculate the UTC date. Enter a double value that is a whole number from

`0`to`24`.**Minutes**Specify the minutes used to calculate the UTC date. Enter a double value that is a whole number from

`0`to`60`.**Seconds**Specify the seconds used to calculate the UTC date. Enter a double value that is a whole number from

`0`to`60`.**Time Increment**Specify the time increment between the specified date and the desired model simulation time. The block adjusts the calculated direction cosine matrix to take into account the time increment from model simulation. For example, selecting

`Day`and connecting a simulation timer to the port means that each time increment unit is one day. The block adjusts its calculation based on that simulation time.This parameter corresponds to the sixth block input, the clock source.

Possible values are

`Day`,`Hour`,`Min`,`Sec`, and`None`. If you select`None`, the calculated Julian date does not take into account the model simulation time. Selecting this option removes the fifth block input.**Action for out of range input**Specify the block behavior when the block inputs are out of range.

Action Description `None`No action. `Warning`Warning in the MATLAB ^{®}Command Window, model simulation continues.`Error`(default)MATLAB returns an exception, model simulation stops. **Higher accuracy parameters**Select this check box to enable the following inputs. These inputs let you better control the conversion result. See Inputs and Outputs for a description.

[ *μ**l**h*]Δ *UT1*Δ *AT*[ *xp*,*yp*][Δδψ, Δδε] or [d *X*,d*Y*]*day***Units**Specifies the parameter and output units:

Units

Position

Equatorial Radius

Altitude

`Metric (MKS)`Meters

Meters

Meters

`English`Feet

Feet

Feet

This option is available only when

**Planet model**is set to`Earth (WGS84)`.**Earth model**Specifies the planet model to use:

`Custom`or`WGS84`.**Flattening**Specifies the flattening of the planet. This option is available only with

**Earth model Custom**.**Equatorial radius**Specifies the radius of the planet at its equator. This option is available only with

**Earth model Custom**.

Input | Dimension Type | Description |
---|---|---|

First | Three-element vector | [ |

Second (Optional) | Scalar | Δ |

Third (Optional) | Scalar | Δ |

Fourth (Optional) | 1-by-2 array | [ |

Fifth (Optional) | 1-by-2 array | If reduction method is `IAU-2000/2006`, this input is the adjustment to the location of the Celestial Intermediate Pole (CIP), specified in radians. This location ([d*X*,d*Y*]) is along the*x*- and*y*-axes, for example,`[-0.2530e-6 -0.0188e-6]`.If reduction method is `IAU-76/FK5`, this input is the adjustment to the longitude ([Δδψ, Δδε]), specified in radians, for example,`[-0.2530e-6 -0.0188e-6]`.
For historical values, see the International
Earth Rotation and Reference Systems Service website ( |

Sixth | Scalar | Time increment, for example, the Clock block. If the |

Output | Dimension Type | Description |
---|---|---|

First | 3-by-1 element vector | Original position vector with respect to the ECI reference system. |

Was this topic helpful?