Many years ago I wrote a Coordinate Geometry (COGO) package for Oracle Sdo_Geometry that contained a Bearing function that, given two points, would return the angle in radians from the horizontal of the vector defined by point A and B.

PostGIS has a similar function called ST_Azimuth.

Here are the relevant declarations of the Bearing function and overloaded ST_Azimuth interfaces.

CREATE OR REPLACE PACKAGE "COGO"
AUTHID CURRENT_USER
As

.........

    /* ----------------------------------------------------------------------------------------
    ** function   : Bearing
    ** precis     : Returns a value between 0 and 2*PI representing the bearing
    **               North = 0, East = PI/2, South = PI, West = 3*PI/4
    **               To convert to degrees multiply by (180/PI).
    ** version    : 1.0
    ** usage      : FUNCTION Bearing( dE1 in number,
    **                               dN1 in number,
    **                               dE2 in number,
    **                               dN2 in number)
    **                        RETURN NUMBER DETERMINISTIC;
    **               eg :new.shape := CODESYS.cogo.Bearing(299900, 5200000, 300000, 5200100);
    ** param      : dE1     : X Ordinate of the start point for the vector
    ** paramtype  : dE1     : NUMBER
    ** param      : dN1     : Y Ordinate of the start point for the vector
    ** paramtype  : dN1     : NUMBER
    ** param      : dE2     : X Ordinate of the end point for the vector
    ** paramtype  : dE2     : NUMBER
    ** param      : dN2     : Y Ordinate of the end point for the vector
    ** paramtype  : dN2     : NUMBER
    ** return     : Bearing : the angle in radians between 0 and 2*PI representing the bearing
    ** rtnType    : Bearing : NUMBER
    ** note       : Does not throw exceptions
    ** note       : Assumes planar projection eg UTM.
    ** @history   : Simon Greener - Feb 2005 - Original coding.
    */
    Function Bearing( dE1 in number,
                      dN1 in number,
                      dE2 in number,
                      dN2 in number)
             Return Number Deterministic;

    /** Alternate binding: 1
    **/
    Function Bearing( startCoord in mdsys.sdo_point_type,
                        endCoord in mdsys.sdo_point_type)
             Return Number Deterministic;

    /** Alternate binding: 2
    **/
    Function Bearing( p_startCoord in mdsys.sdo_point_type,
                        p_endCoord in mdsys.sdo_point_type,
                     p_planar_srid in number,
                 p_geographic_srid in number := 8311
	                  )
     Return Number Deterministic;

    /* Alternate binding for SQL/MM
    **/
    Function ST_Azimuth( p_startCoord in mdsys.ST_Point,
                         p_endCoord   in mdsys.ST_Point)
      Return Number Deterministic;

.....

END Cogo;

Now, some examples of the use of these functions.

/* What happens when NULL points are provided */
SELECT COGO.Bearing(NULL,NULL) 
  FROM DUAL;

AZIMUTH
----------------------
NULL

1 rows selected

/* What happens if start and end point are the same? */
SELECT ROUND(COGO.Bearing(mdsys.sdo_point_type(1,2,null), mdsys.sdo_point_type(1,2,null)) / ( 2 * Constants.pi ) * 360) as degAz
  FROM DUAL;

DEGAZ
----------------------
NULL

1 rows selected

/* PostGIS example */
SELECT ST_Azimuth(ST_MakePoint(1,2), ST_MakePoint(3,4))/(2*pi())*360 as degAz, 
       ST_Azimuth(ST_MakePoint(3,4), ST_MakePoint(1,2))/(2*pi())*360 As degAzrev

degaz	degazrev
------	---------
45      225

/* Oracle version of PostGIS example using "native" interfaces */
SELECT ROUND(COGO.Bearing(mdsys.sdo_point_type(1,2,null), mdsys.sdo_point_type(3,4,null)) / ( 2 * Constants.pi ) * 360) as degAz,
       ROUND(COGO.Bearing(mdsys.sdo_point_type(3,4,null), mdsys.sdo_point_type(1,2,null)) / ( 2 * Constants.pi ) * 360) as degAzRev
  FROM DUAL;

DEGAZ                  DEGAZREV
---------------------- ----------------------
45                     225

1 rows selected

/* PostGIS example using "equivalent" ST_* interfaces */
SELECT Round(Cogo.ST_Azimuth(mdsys.ST_Point(1,2), mdsys.ST_Point(3,4))/(2*Constants.pi)*360) as degAz, 
       Round(Cogo.ST_Azimuth(mdsys.ST_Point(3,4), mdsys.ST_Point(1,2))/(2*Constants.pi)*360) As degAzrev
  FROM dual;

DEGAZ                  DEGAZREV
---------------------- ----------------------
45                     225

1 rows selected

I hope this is useful to someone.

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