2.7.6 Oriented Point

An oriented point is a special type of point geometry that includes coordinates representing the locations of the point and a virtual end point, to indicate an orientation vector that can be used for rotating a symbol at the point or extending a label from the point. The main use for an oriented point is in map visualization and display applications that include symbols, such as a shield symbol to indicate a highway.

To specify an oriented point:

• Use an SDO_GTYPE value (explained in SDO_GTYPE) for a point or multipoint geometry.

• Specify a null value for the SDO_POINT attribute.

• In the SDO_ELEM_INFO array (explained in SDO_ELEM_INFO), specify an additional triplet, with the second and third values (SDO_ETYPE and SDO_INTERPRETATION) as 1 and 0. For example, a triplet of 3,1,0 indicates that the point is an oriented point, with the third number in the SDO_ORDINATES array being the first coordinate, or x-axis value, of the end point reflecting the orientation vector for any symbol or label.

• In the SDO_ORDINATES array (explained in SDO_ORDINATES), specify the coordinates of the end point for the orientation vector from the point, with values between -1 and 1. The orientation start point is assumed to be (0,0), and it is translated to the ___location of the physical point to which it corresponds.

Figure 2-8 illustrates an oriented point geometry at coordinates (12,14), with an orientation vector of approximately 34 degrees (counterclockwise from the x-axis), reflecting the orientation coordinates 0.3,0.2. (To have an orientation that more precisely matches a specific angle, refer to the cotangent or tangent values in the tables in a trigonometry textbook.) The orientation vector in this example goes from (0,0) to (0.3,0.2) and extends onward. Assuming i=0.3 and j=0.2, the angle in radians can be calculated as follows: angle in radians = arctan (j/i). The angle is then applied to the physical point associated with the orientation vector.

Figure 2-8 Oriented Point Geometry

Description of "Figure 2-8 Oriented Point Geometry"

In the SDO_GEOMETRY definition of the geometry illustrated in Figure 2-8:

• SDO_GTYPE = 2001. The 2 indicates two-dimensional, and the 1 indicates a single point.

• SDO_SRID = NULL.

• SDO_POINT = NULL.

• SDO_ELEM_INFO = (1,1,1, 3,1,0). The final 1,0 in 3,1,0 indicates that this is an oriented point.

• SDO_ORDINATES = (12,14, 0.3,0.2). The 12,14 identifies the physical coordinates of the point; and the 0.3,0.2 identifies the x and y coordinates (assuming 12,14 as the origin) of the end point of the orientation vector. The resulting orientation vector slopes upward at about a 34-degree angle.

Example 2-12 shows a SQL statement that inserts the geometry illustrated in Figure 2-8 into the database.

INSERT INTO cola_markets VALUES(
  91, 
  'oriented_point', 
  SDO_GEOMETRY(
    2001, 
    NULL, 
    NULL, 
    SDO_ELEM_INFO_ARRAY(1,1,1, 3,1,0), 
    SDO_ORDINATE_ARRAY(12,14, 0.3,0.2)));

-- Oriented multipoint: 2 points, different orientations
INSERT INTO cola_markets VALUES(
  92,
  'oriented_multipoint',
  SDO_GEOMETRY(
    2005, -- Multipoint
    NULL,
    NULL,
    SDO_ELEM_INFO_ARRAY(1,1,1, 3,1,0, 5,1,1, 7,1,0),
    SDO_ORDINATE_ARRAY(12,14, 0.3,0.2, 12,10, -1,-1)));