This task shows you how to create a curve that is parallel to a reference curve.
Open the ParallelCurves1.CATPart document.
1. Click the Parallel Curve icon .
The Parallel Curve Definition dialog box appears.
2. Select the reference Curve to be offset.
3. Select the Support plane or surface on which the reference curve lies.
4. Specify the offset of the parallel curve either by:
❍ entering a value or using the graphic manipulator in the Constant field.
❍ selecting a point in the Point field (in both Geodesic and Euclidean mode) In that case, the Constant field is grayed.
5. Choose the parallelism mode to create the parallel curve.
❍ Euclidean: the distance between both curves will be the shortest possible one, regardless of the support.
If you select this mode, you can choose to offset the curve at a constant distance from the initial element, or according to a law. In this case, you need to select a law as defined in Creating Laws.
Defining Laws
The law can be negative, providing the curves are curvature continuous. Note that:
- it is advised to use curvature continuous laws, - it is advised not to use laws with a vertical tangency,
- it is possible to create a parallel curve with a law that reverses (which means becoming either positive or negative) only on a curve that is tangency continuous.
■ Click the Law... button to display the Law Definition dialog box. The 2D viewer enables you to previsualize the law evolution before applying it.
■ Enter Start and End values. ■ Choose the law type.
Four law types are available:
a. Constant: a regular law, only one value is needed.
b. Linear: a linear progression law between the Start and End indicated values c. S type: an S-shaped law between the two indicated values
d. Advanced: allowing to select a Law element as defined in Creating Laws.
For the S type, you need to define a second value. The distance will vary between these two values, over the specified number of revolutions.
■ The Law Viewer allows you to:
- visualize the law evolution and the maximum and minimum values, - navigate into the viewer by panning and zooming (using to the mouse), - trace the law coordinates by using the manipulator,
- change the viewer size by changing the panel size - fit all in by using the viewer contextual menu
- change the law evaluation step by using the viewer contextual menu (from 0.1 (10 evaluations) to 0.001 (1000 evaluations)).
■ Check the Inverse law button to reverse the law as defined using the above options. ■ Click OK to return to the Parallel Curve Definition dialog box.
❍ Geodesic: the distance between both curves will be the shortest possible one, taking the support curvature into account. In this case, the offset always is constant in every points of the curves and you do not need to select a corner type.
6. Select corner type (useful for curves presenting sharp angles):
❍ Sharp: the parallel curve takes into account the angle in the initial curve
❍ Round: the parallel curve is rounded off as in a corner
In this case, the offset always is constant in every points of the curves and you do not need to select a corner type.
This type is only effective with acute angles, not with obtuse or re-entrant angles. It corresponds to the trace left by a ball rolling on a profile.
The parallel curve is displayed on the support surface and normal to the reference curve.
8. Click OK to create the parallel curve.
The curve (identified as Parallel.xxx) is added to the specification tree.
Parallel curve defined by an constant offset value: Parallel curve defined by a passing point:
Parameters can be edited in the 3D geometry. To have further information, please refer to the Editing Parameters
chapter.
Optional Parameters
● You can use the Reverse Direction button to display the parallel curve on the other side of the reference curve or click the arrow directly on the geometry.
● When the selected curve is a planar curve, its plane is selected by default. However, you can explicitly select any support.
● when you modify an input value through the dialog box, such as the offset value or the direction, the result is computed only when you click on the Preview or OK buttons.
● Would the value be inconsistent with the selected geometry, a warning message is displayed, along with a warning sign onto the geometry. If you move the pointer over this sign, a longer message is displayed to help you continue with the operation.
● Check the Both Sides button to create two parallel curves, symmetrically in relation to the selected curve, and provided it is compatible with the initial curve's curvature radius.
The second parallel curve has the same offset value as the first parallel curve. In that case it appears as aggregated under the first element.
Therefore both parallel curves can only be edited together and the aggregated element alone cannot be deleted.
If you use the Datum mode, the second parallel is not aggregated under the first one, but two datum elements are created.
● Use the Repeat object after OK checkbox to create several parallel curves, each separated from the initial curve by a multiple of the offset value.
● The options set in the dialog box are retained when exiting then returning to the Parallel curve function.
Smoothing the curve
You can smooth the curve by checking either:
● None: deactivates the smoothing result
With a support surface:
● Tangency: enhances the current continuity to tangent continuity ● Curvature: enhances the current continuity to curvature continuity
You can specify the maximum deviation for G1 or G2 smoothing by entering a value or using the spinners.
In the case of an Euclidian parallel curve, only small discontinuities are smoothed, especially discontinuities that are introduced during the parallel operation.
Moreover, a topology simplification is automatically performed for G2 vertices: cells with a curvature continuity are merged.
Without support surface:
● 3D Smoothing: the smoothing is performed without specifying any support surface. As a consequence, the resulting smoothed curve has a better continuity quality and is not exactly laid down on the surface.
As a consequence, you may need to activate the Tolerant laydown option. Refer to the Customizing General Settings chapter. This option is available if you previously select the Tangency or Curvature smoothing type.
Open the ParallelCurves2.CATPart document.