7 General message format and information elements coding

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.

7.1 Overview

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

Bits

4 3 2 1

0 0 0 0

Ellipsoid Point

0 0 0 1

Ellipsoid point with uncertainty Circle

0 0 1 1

Ellipsoid point with uncertainty Ellipse

0 1 0 1

Polygon

1 0 0 0

Ellipsoid point with altitude

1 0 0 1

Ellipsoid point with altitude and uncertainty Ellipsoid

1 0 1 0

Ellipsoid Arc

other values

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)

7.3.4 Polygon

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

Altitude

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

Ellipsoid Arc

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

Start angle

Bit 8 of octet 9 is the low order bit

Stop angle

Bit 1 of octet 9 is the high order bit

Inner radius

Bit 8 of octet 8 is the high order bit

Bit 1 of octet 912 is the low order bit