### astCurve

Draw a geodesic curve

#### Description:

This function draws a geodesic curve between two points in the physical coordinate system of a Plot. The curve drawn is the path of shortest distance joining the two points (as defined by the astDistance function for the current Frame of the Plot). For example, if the current Frame is a basic Frame, then the curve joining the two points will be a straight line in physical coordinate space. If the current Frame is more specialised and describes, for instance, a sky coordinate system, then the geodesic curve would be a great circle in physical coordinate space passing through the two sky positions given.

Note that the geodesic curve is transformed into graphical coordinate space for plotting, so that a straight line in physical coordinates may result in a curved line being drawn if the Mapping involved is non-linear. Any discontinuities in the Mapping between physical and graphical coordinates are catered for, as is any clipping established using astClip.

If you need to draw many geodesic curves end-to-end, then the astPolyCurve function is equivalent to repeatedly using astCurve, but will usually be more efficient.

If you need to draw curves which are not geodesics, see astGenCurve or astGridLine.

#### Synopsis

void astCurve( AstPlot $\ast$this, const double start[], const double finish[] )

#### Parameters:

##### this
Pointer to the Plot.
##### start
An array, with one element for each axis of the Plot, giving the physical coordinates of the first point on the geodesic curve.
##### finish
An array, with one element for each axis of the Plot, giving the physical coordinates of the second point on the geodesic curve.

#### Notes:

• No curve is drawn if either of the " start" or " finish" arrays contains any coordinates with the value AST__BAD.

• An error results if the base Frame of the Plot is not 2-dimensional.

• An error also results if the transformation between the current and base Frames of the Plot is not defined (i.e. the Plot’ s TranInverse attribute is zero).