# Position Covariance

Depending on the type of Position Covariance data provider selected, you can:

- Compute 3D position covariance for a vehicle in a specified set of coordinate axes.
- Compute 2D cross section or projection of position covariance for a vehicle in a specified coordinate plane.
- Compute 2D cross section or projection of position covariance for a missile at impact in a plane perpendicular to the missile's central body fixed velocity. The resulting 2D ellipse is then re-projected along the fixed velocity onto the local-horizontal plane.

Scale and probability both affect the size of the covariance ellipsoid. The scale is a direct multiplier of the covariance size. The probability is related to scale: covariance is scaled in order to ensure that it encompasses volume such that the position appears inside it with the desired probability.

SEP Probability stands for “spherical error probable” probability. It affects SEP and Appx. SEP elements of the data provider. SEP determines the radius of a sphere whose volume is such that the position appears inside this sphere with the desired probability.

CEP Probability stands for “circular error probable” probability. It affects CEP and Appx. CEP elements of the data provider. CEP determines the radius of a circle whose area is such that the position appears inside this circle with the desired probability when it passes through the plane of this circle.