Creating Non-Planar Curves by Projection

This is done using the Non-Planar (Projected) page of the Create New Curve dialog.

Figure 3:77. Dialog page for creating non-planar curves by projecting Clines onto existing curves

The new curve's data points are found by projecting a Cline onto the set of existing curves. The Cline is projected in the direction normal to the plane that it lies in. In other words, the points generated will appear to lie on the Cline when viewed in this direction. This is the same functionality that is available in Lines (see Creating 3D Curves).

There are three possible sources for the Cline that is to be projected:

• An existing Cline, selected from the drop-down box.

• A new Cline created from a sequence of selected points.

• A new Cline created by digitizing points ‘Free-hand’.

If creating a new Cline, a sequence of two of more points must be selected. These can be data points from existing curves, or intersection points between curves (as for creating non-planar curves from points). The direction in which to project the Cline is also chosen - the orthogonal plane that the Cline will lie in is defined as being normal to this. The new Cline is fitted to data points that are formed by projecting the selected sequence of points into this orthogonal plane. If the Keep Cline box is checked, the new Cline will given the same name as the non-planar curve, and added to the set of curves. Otherwise, it will be discarded once the projection has taken place.

If an existing Cline is selected, the projection direction is fixed (normal to the plane that it lies in).

The Interpolation checkboxes control which of the orthogonal curve types are used to create data points in the projection process. Other curve types (Plines, Tangents, Knuckles ) are always used.

The Limits controls are used to specify a range over which the new curve's data points will be defined. This range is measured along the axis parallel to the direction of projection. Effectively, this specifies two parallel planes normal to the direction of projection. Only data points that lie between these planes will be used to create the new curve. This is particularly useful when projecting Clines that lie in the x-plane (section view), and the extent of the curve needs to be contained within the fore or afterbody of the vessel.

If there is more than one way that the curve could be created, the user is presented with a Options dialog.

Figure 3:78. Options when creating a non-planar curve by projecting a Cline

The options are as follows:

• (Re)create by projection causes the curve’s data points to be created by projecting a Cline onto the other curves. This is usually what is intended.

• Activate and use is an option when a curve with the same name already exists, but is inactive. If this option is chosen, this curve is simply activated (no geometry changes occur).

If Cancel is clicked, the curve creation is aborted.