Data Bar - Data Points Grid - Tangent Angles at Data Points

One end of a curve is the 'first point' and the other end the 'last point'. This gives a sense of direction to the curve. In this light, a curve that passes through a data point can be thought of as running into the point on one side, and running out of it on the other. If this data point represents a tangent discontinuity (a knuckle), then there are two different tangent directions at the point - one on the side running into the point ('pre-tangent'), the other on the side running out of the point ('post-tangent'). By specifying the data point to be a particular type of knuckle, the user can choose whether or not to control either of these tangents.

If there is tangent continuity at the data point, then there is only one tangent direction. This is the situation for data points of type Tangent. Here, the tangent information is specified in the 'pre-tangent' columns of the grid.

Tangents are specified in the grid cells in terms of rotation angles about the x, y and z axes. The valid range is -180° to 180° (other specified angles are converted to this range).

Tangent angle definition

The definition of the 3 angles is illustrated below:

If the direction of a tangent is parallel to any of the axes, one of the angles will be undefined. This is indicated by an entry of '####' in the relevant cell.

Note:
For 3d curves (Plines, Knuckles, Tangents ), care must be taken to ensure that tangency controls lie within a constant x, y or z plane. This problem does not arise with curves that lie in any of the orthogonal planes, such as sections and waterlines. Most of these curves are locked in the axis that is normal to the plane that they lie in, so only one rotation angle can be specified anyway (see Locked Axes).

See Curves Graphical Reference for further information about data point behavior.