03.323GPPRelease 98TSUniversal Geographical Area Description (GAD)
This clause describes a coding method for geographical area descriptions. A geographical area description is coded as a finite bit string. In the figures, the bit string is described by octets from top downward, and in the octet from left to right. Number encoding strings start with the most significant bit.
A bit string encoding a geographical description shall consist of the following parts:
– Type of Shape;
– Shape Description.
Such a bit string is usually part of an information element. The structure of the information element (e.g., element identifier, length) depends on the protocol in which the message containing the description is defined, and is specified in the protocol specification.
This organisation is illustrated in the example shown in figure 4.
Figure 4: Example
7.2 Type of Shape
The Type of Shape information field identifies the type which is being coded in the Shape Description. The Type of Shape is coded as shown in table 2.
Table 2: Coding of Type of Shape
4 3 2 1
0 0 0 0
0 0 0 1
Ellipsoid point with uncertainty Circle
0 0 1 1
Ellipsoid point with uncertainty Ellipse
0 1 0 1
1 0 0 0
Ellipsoid point with altitude
1 0 0 1
Ellipsoid point with altitude and uncertainty Ellipsoid
1 0 1 0
reserved for future use
7.3 Shape description
The shape description consist of different elements.
7.3.1 Ellipsoid Point
The coding of a point is described in figure 5.
Figure 5: Shape description of a point
S: Sign of latitude
Bit value 0 North
Bit value 1 South
Degrees of latitude
Bit 1 of octet 4 is the low order bit
Degrees of longitude
Bit 1 of octet 7 is the low order bit
7.3.2 Ellipsoid Point with uncertainty Circle
Figure 6: Shape description of an ellipsoid point with uncertainty circle
7.3.3 Ellipsoid Point with uncertainty Ellipse
Figure 6a: Shape description of an ellipsoid point with uncertainty ellipse
Orientationof major axis
angle in degrees between the major axis and north
(0 = north, 90 = east, values of 180 and above are not used)
Figure 7: Shape description of a polygon
The number of points field encodes in binary on 4 bits the number n of points in the description, and ranges from 3 to 15.
7.3.5 Ellipsoid Point with Altitude
The coding of an ellipsoid point with altitude is described in figure 8.
Figure 8: Shape description of an ellipsoid point with altitude
D: Direction of Altitude
Bit value 0 Altitude expresses height
Bit value 1 Altitude expresses depth
Bit 1 of octet 9 is the low order bit
7.3.6 Ellipsoid Point with altitude and uncertainty ellipsoid
Figure 9: Shape description of an ellipsoid point with altitude and uncertainty ellipsoid
Editorial Note: T1P1.5 intends to align the Arc shape with ITU-T Q.762, Q.763
Figure 10: Shape description of an Ellipsoid arc
Bit 8 of octet 9 is the low order bit
Bit 1 of octet 9 is the high order bit
Bit 8 of octet 8 is the high order bit
Bit 1 of octet 912 is the low order bit