### astDistance

Calculate the distance between two points in a Frame

#### Description:

This function finds the distance between two points whose Frame coordinates are given. The distance calculated is that along the geodesic curve that joins the two points.

For example, in a basic Frame, the distance calculated will be the Cartesian distance along the straight line joining the two points. For a more specialised Frame describing a sky coordinate system, however, it would be the distance along the great circle passing through two sky positions.

#### Synopsis

double astDistance( AstFrame $\ast$this, const double point1[], const double point2[] )

#### Parameters:

##### this
Pointer to the Frame.
##### point1
An array of double, with one element for each Frame axis (Naxes attribute) containing the coordinates of the first point.
##### point2
An array of double, with one element for each Frame axis containing the coordinates of the second point.

#### Returned Value

##### astDistance
The distance between the two points.

#### Notes:

• This function will return a " bad" result value (AST__BAD) if any of the input coordinates has this value.

• A " bad" value will also be returned if this function is invoked with the AST error status set, or if it should fail for any reason.