Go to content Go to navigation and search

Home

Current SQL Server Blog Articles


Search

Browse

RSS / Atom

Email me

textpattern

Creative Commons License
All Blog Articles, Data Models and Free Source Code by Simon Greener, The SpatialDB Advisor is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License.

COGO: Create point from bearing and distance

Friday May 06 2011 at 03:15

Sometimes the definition of an object can be as a bearing and distance from a known point. This often happens in unbiased statistical sampling, or when creating polygons describing land titles from coordinate geometry (COGO) measurements.

Here is a version of the PointFromBearingAndDistance PL/SQL function I wrote for Oracle Spatial many years ago for SQL Server 2008.

Note that I have a schema call cogo in which I create functions like this. You can use anything you like.

/**
* @function   : PointFromBearingAndDistance
* @precis     : Returns a point geometry given a starting point, bearing and distance.
* @version    : 1.0
* @usage      : FUNCTION PointFromBearingAndDistance(@p_dStartE   float,
*                                                    @p_dStartN   float,
*                                                    @p_dBearing  float,
*                                                    @p_dDistance float,
*                                                    @p_precision int = 3,
*                                                    @p_srid      int = 0 )
*                 RETURNS GEOMETRY
*               eg select cogo.PointFromBearingAndDistance(0,0,45,100,3,0).STAsText();
* @param      : p_dStartE     : X Ordinate of start point of bearing
* @paramtype  : p_dStartE     : FLOAT
* @param      : p_dStartN     : Y Ordinate of start point of bearing
* @paramtype  : p_dStartN     : FLOAT
* @param      : p_dBearing    : Whole circle bearing (ie 0 North to 360 degree clockwise rotation)
* @paramtype  : p_dBearing    : FLOAT
* @param      : p_dDistance   : Distance in projection units from point along bearing
* @paramtype  : p_dDistance   : FLOAT
* @param      : p_precision   : Precision of any XY value ie number of significant digits. If null then 3 is assumed (ie 1 mm): 3456.2345245 -> 3456.235 
* @paramtype  : p_precision   : INTEGER
* @param      : p_srid        : SRID of output shape
* @paramtype  : p_srid        : INTEGER
* @return     : geometry      : Point geometry 
* @rtnType    : geometry      : GEOMETRY
* @note       : Does not throw exceptions
* @note       : Assumes planar projection eg UTM.
* @history    : Simon Greener  - Feb 2005 - Original coding.
* @history    : Simon Greener  - May 2011 - Converted to SQL Server
*/
CREATE FUNCTION 
[cogo].[PointFromBearingAndDistance] (@p_dStartE   Float,
                                      @p_dStartN   Float,
                                      @p_dBearing  Float,
                                      @p_dDistance Float,
                                      @p_precision int = 3,
                                      @p_srid      int = 0 )
RETURNS geometry
AS
Begin
  Declare
      @dAngle1    Float,
      @dAngle1Rad Float,
      @dDeltaN    Float,
      @dDeltaE    Float,
      @dEndE      Float,
      @dEndN      Float,
      @precision  int = CASE WHEN @p_precision IS NULL THEN  3 ELSE @p_precision END,
      @srid       int = CASE WHEN @p_srid      IS NULL THEN  0 ELSE @p_srid      END;
  BEGIN
      IF ( @p_dStartE   IS NULL OR
           @p_dStartN   IS NULL OR
           @p_dBearing  IS NULL OR
           @p_dDistance IS NULL )
      RETURN NULL;
 
      -- First calculate dDeltaE and dDeltaN
      IF ( @p_dBearing < 90 )
      BEGIN
          SET @dAngle1    = 90 - @p_dBearing;
          SET @dAngle1Rad = @dAngle1 * PI() / 180;
          SET @dDeltaE    = Cos(@dAngle1Rad) * @p_dDistance;
          SET @dDeltaN    = Sin(@dAngle1Rad) * @p_dDistance;
      END
      IF ( @p_dBearing < 180 )
      BEGIN
          SET @dAngle1    = @p_dBearing - 90;
          SET @dAngle1Rad = @dAngle1 * PI() / 180;
          SET @dDeltaE    = Cos(@dAngle1Rad) * @p_dDistance;
          SET @dDeltaN    = Sin(@dAngle1Rad) * @p_dDistance * -1;
      END
      IF ( @p_dBearing < 270 )
      BEGIN
          SET @dAngle1    = 270 - @p_dBearing;
          SET @dAngle1Rad = @dAngle1 * PI() / 180;
          SET @dDeltaE    = Cos(@dAngle1Rad) * @p_dDistance * -1;
          SET @dDeltaN    = Sin(@dAngle1Rad) * @p_dDistance * -1;
      END
      IF ( @p_dBearing <= 360 )
      BEGIN
          SET @dAngle1    = @p_dBearing - 270;
          SET @dAngle1Rad = @dAngle1 * PI() / 180;
          SET @dDeltaE    = Cos(@dAngle1Rad) * @p_dDistance * -1;
          SET @dDeltaN    = Sin(@dAngle1Rad) * @p_dDistance;
      End 
      -- Calculate the easting and northing of the end point
      SET @dEndE = @dDeltaE + @p_dStartE;
      SET @dEndN = @dDeltaN + @p_dStartn;
      RETURN geometry::Point(ROUND(@dEndE, @precision),ROUND(@dEndN, @precision), @srid);
    END;
END
GO

Here is an example of how to generate the geometry::Point object at the end of a bearing of 45 degrees and distance of 100 meters from ( 0,0 ) .

select cogo.PointFromBearingAndDistance(0,0,45,100,3,0).STAsText() as NewPoint;

NewPoint
POINT (70.711 70.711)


Or more visually:

DECLARE
  @XY Float = SQRT(POWER(100,2)/2);
select geometry::STGeomFromText('POINT(0 0)',0).STBuffer(10) as geom
union all
select geometry::STGeomFromText('LINESTRING(0 0,' + STR(@XY,10,5) + ' ' + STR(@XY,10,5) + ')',0) as geom
union all
select cogo.PointFromBearingAndDistance(0,0,45,100,3,0).STBuffer(10) as geom;

I hope this is helpful to someone.

Creative Commons License

post this at del.icio.uspost this at Diggpost this at Technoratipost this at Redditpost this at Farkpost this at Yahoo! my webpost this at Windows Livepost this at Google Bookmarkspost this to Twitter

Comment