as_unitvec.hxx

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// Header for unit_vector.

// Unit vectors work just like vectors, and so are a derived type.  


#if !defined( UNITVEC_CLASS )
#define UNITVEC_CLASS

#include "as_vector.hxx"

class transf;
class interval;


class  unit_vector: public vector {

public:

	unit_vector() {}	// allow unitialised unit_vectors


	// Construct a unit vector from three components. 
	// Always normalises result.

	unit_vector( double, double, double );


	// Construct a unit vector from an array of three doubles. 
	// Always normalises result.

	unit_vector( double u[ 3 ] );


	// Unary minus.

	friend  unit_vector operator-( unit_vector const & );


	// Scalar product of a position. This is just as for a vector,
	// but declared explicitly to avoid an ambiguity.

	friend  double operator%( position const &, unit_vector const & );
	friend  double operator%( unit_vector const &, position const & );


	// Find a position as the cross-product of a position with a 
	// unit vector.

	friend  position operator*( position const &, unit_vector const & );
	friend  position operator*( unit_vector const &, position const & );


	// The only way to get back from a vector to a unit_vector is by
	// means of normalise().  We make it explicit, and have no 
	// constructor from vector to unit_vector in order to make clear 
	// the change in value.

	friend  unit_vector normalise( vector const & );


	// Transform a unit vector by the rotation matrix in a 
	// transformation (gives an error if the transformation contains
	// a shear).

	friend  unit_vector operator*( unit_vector const &, transf const & );
	friend  unit_vector operator*( unit_vector const &, transf const * );
	unit_vector const &operator*=( transf const & );

};


// Standard axis vectors: (1,0,0), (0,1,0), (0,0,1)

extern  unit_vector x_axis, y_axis, z_axis;

// Zero length "unit vector", used for signalling exceptional
// conditions.

#endif