Project on NURBS Surface

When you choose Draw->Project on NURBS Surface command in the Model module, you can project a NURBS curve onto a NURBS surface and then model with that curve.

Using a combination of modelling techniques, you can achieve some quick and interesting results. For example, after projecting a curve onto a surface, extract the projected surface curve, extrude it, and modify the generated objects using relational modelling.

Note:

When you model with the projected curve, you do not affect the underlying surface at all.
By contrast Draw->Trim NURBS Surface also projects curves onto a NURBS surface in the same way, but achieves very different results.

Both processes are described, with examples and detailed procedures in Modelling NURBS Surfaces with Projected Curves of the Modelling User's Guide.

Procedure

This is the basic process to follow:

1. Select a NURBS surface object.
2. Select a closed NURBS curve.
3. Position the curve in relation to the target surface; for example, translate it, scale it, or rotate it to the desired angle.
4. Select the target surface, choose Draw->Project on NURBS Surface, and pick the source curve. The Project on NURBS Surface dialogue box is displayed.
5. Accept the default settings or enter new ones for the following:

• The Projection Method and coordinate system you want to apply. You can verify the projection angle in the windows.
• Increase or decrease the Sampling data, if you like.

  6. You can always preview the results before projecting.

• When you click Preview, all the curves projected on the surface are listed in the Projected curves scroll box.
• You can click Ok to project all of them, or select a specific one to project.

Tip:
The best way to verify your selection is to check which curve is currently highlighted in the window

6. You can delete projected curves using the Draw->Delete Projected Curves command.

Parameters

Projection Method

Note:

Examples of the various projection methods and their results are provided in Projection Methods of the Modelling User's Guide.

Parallel

With parallel projection, the projection source is infinity and as a result, the projection rays remain parallel. You need only specify the direction of the ray. The size of the projected curve on the surface depends on the position and shape of the surface.

• X, Y, Z axis makes the projection along the selected axis direction in the Coordinates system option selected (local or global).
• User direction specifies a user-defined projection direction in the Coordinates system selected (local or global). If you select the User direction option, enter the X, Y, or Z components of the direction line.

Perspective

With perspective projection, the source curve is projected onto the surface by a projection ray originating from a point at the surface centre or any user-defined point.

Following the rules of perspective, the source curve is projected onto the surface at a different size according to the relative distance and angle of the projection source.

• Surface center projects the source curve onto the NURBS surface from a point at the centre of the surface.
• User center specifies any point as the source from which to project the source curve onto the NURBS surface. Enter the XYZ coordinates of the point, using either coordinates local to the surface or global coordinates.

Coordinates

Select either the default local or global coordinate system for the projection method used.

• Local uses the coordinate system local to either the target surface or the source curve as follows:
• If you selected either XYZ axis or User direction (Parallel projection), these coordinates are local to the source curve.
• If you selected User center (Perspective projection), these coordinates are local to the target surface.
• Global uses the global coordinate system.

Sampling

Sets the resolution of the projected curve on the surface. The higher the number, the smoother the trim region.

By default, this value is set to the same step number as the curve to be projected. You should leave it close to this value to achieve the highest level of fidelity between the source curve and the surface curve.

Click this button to display the Curve Info dialogue box and change the Step value if necessary.

Projected Curves

If you click Preview, the Projected Curves box lists all the potential surface curves created by the preview operation.

By default, all curves in the list are selected for use in the operation. You can select which surface curves you wish to keep and discard the rest.

The numbering sequence in the list may not match the apparent sequence on the target surface; For example, Proj # 3 in the list may correspond to what appears to be curve 2 on the target surface. This is not significant: use the highlighted curve on the target surface to make sure you are selecting the desired surface curve.

Left-click to select or deselect a curve in the scroll box, or press
Shift and left-click to select/deselect multiple curves. Verify the current curve selection using the magenta colour in the windows.

Note:

The NURBS Surface Info dialogue box displays a numbered list of projected and trim curves. The number of curves listed may not be the same, depending on whether a trim curve intersected surface boundaries.

Preview

Displays the result of the operation without closing the dialogue box. The potential surface curves are listed and numbered in the Projected curves scroll box.

You may modify some of the parameters, preview the results, and repeat until you are satisfied and then click Ok to complete the operation and close the dialogue box.

Cancel

Cancels the projection operation and exits the dialogue box without applying the settings.

Ok

Applies the settings and exits the dialogue box.

Last updated 08-apr-1998