﻿ Shapes: Planes # Shapes: Planes A plane shape is an infinite plane surface, defined by specifying a point on the plane and the maximum slope angle and direction of the plane.

### Slope angle, slope direction

The slope angle is the angle of elevation of the line of maximum slope, relative to the $xy$-plane of the connection axes; the slope direction is the direction of the line of maximum upwards slope, again relative to the $xy$-plane of the connection axes. For example, if the plane were fixed relative to the global coordinate system, then a slope angle of 0° would represent a horizontal plane, whereas a slope angle 90° would represent a vertical plane. Similarly, a slope angle of 30° and a slope direction of 90° indicate that the plane slopes upwards in the positive $y$-direction at 30° to the $xy$-plane of the connection axes.

The inside of a plane is on the negative $z$ side (i.e. below, for a fixed or anchored plane) if the slope angle is in the range -90° to +90°, and on the positive $z$ side (i.e. above for a fixed or anchored plane) otherwise.

The remaining plane data, including its position, are common to all geometric shapes and are described under the shape data and drawing topics.