User Guide

User Guide

User Guide

Place Free-form Surface

(3D only) Used to place or construct a free-form B-spline surface.

Tool Setting	Effect
Method	Sets how the surface is generated. Define Poles — Poles (vertices) of the control net are defined by data points or vertices of elements. The number of poles in the u- and v-direction must be greater than or equal to the order in that direction. Through Points — Surface passes through the points defined by the data points or vertices of elements and is interpolated at each point. One pole is defined for each data point, the number of which must be greater than or equal to the Order. L-Square By Tol — The surface is approximated based on the points defined by the data points or the vertices of the identified line string or shape. The maximum deviation of the input points from the surface is adjustable using the Tolerance setting. After the approximation surface is created, the maximum deviation and the mean deviation are displayed in the status field. L-Square By Num — The sum of the squares of the distances from the data points or vertices of elements to corresponding points on the surface is minimized. The control net has the active number of Poles in the u- and v-direction. If the maximum error exceeds the Tolerance, the maximum error is displayed in the status bar. see footnote 99 Catmull-Rom — Fourth-order NURBS surface that is interpolated to closely resemble the overall shape defined by the data points entered or vertices of the selected line strings.
Define By	Sets how the surface is created. Placement — The surface is placed by entering data points. Construction — The surface is constructed based on the vertices of line strings or shapes.
Closure	Sets whether surface is Open or Closed in the u- or v-direction.
Order	The order of the equation that defines the surface in the u- or v-direction (2-15).
Poles	The number of poles in the u- or v-direction, if Method is L-Square By Num (2–101).
Tolerance	Sets the fitting or approximation tolerance, when Method is set to L-Square By Tol. The minimum distance from any one of the input data points to the surface is less than this value. The minimum distance is computed by projecting a point to the surface.

To place a free-form surface with data points

Select Place Free-form Surface tool.

Set Define By to Placement.

Enter a series of data points to define the first row (in the u-direction).

Method	Each data point defines
Define Poles	One of the control net's poles.
Through Points	A point through which the surface must pass.
L-Square By Tol or L-Square By Num	One of a set of points that is approximated.

Reset to complete the first row.
The number of data points in the first row must be greater than or equal to the Order in the u-direction.

Enter more data points to define other rows. After the same number of data points as in the first row is entered, the row is completed and a new row is started.

Reset to complete the definition.
If at least as many rows as the Order in the v-direction are completely defined, a B-spline surface is generated.


Placing a free-form surface by entering data points (Method set to Define Poles). A Reset was entered after data points 4 and 12.

To construct a free-form surface based on an element's vertices

Select the Place Free-form Surface tool.

Set Define By to Construction.

Identify the elements in the sequence that the B-spline surface is to follow.

Accept the B-spline surface.

Alternative Method — To construct a free-form surface based on an element's vertices

Use the Element Selection tool to select the elements in the sequence that the B-spline surface is to follow.

Select the Place Free-form Surface tool.

Accept the B-spline surface.


Left: Identify the elements, in the sequence that the B-spline surface is to follow (points 1 to 4). Right: Accept (5) to create the B-spline surface.


Rendered view of the B-spline surface.

Key-in: PLACE SURFACE