Directions

Directions are required to specify the directions of lines. The direction is defined as the angle between the positive u-axis of the coordinate system and the positive direction of the line. It is positive in the positive circulation direction.

Directions are given as angles when restricted lines are created using coordinates in the local coordinate system (U, V, ). For unrestricted lines using global coordinates (X,Y,Z) an additional "direction point" is used.

(For directions perpendicular to the axes of the coordinate systems there are certain rules, see below)

<direction_angle>::=<angle> | <top_ref>

<angle>::=<number>

<top_ref>::=P|TA|TB<start> [([<step>])] <step> [+|-<delta>]

The general layout of reference to the direction of a topology point is the same as for coordinate references.

Prefixes P and TA have the same meaning and mean reference to the primary direction of the topology point. TB means reference to the secondary direction.

Examples (of angles):