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The Draw->Curve commands in the Model module let you draw NURBS,
Linear, Bezier, Cardinal, and B-Spline curves. See Curves of the Modelling
User's Guide for an overall description of curves and how to use them.
The direction in which you draw curves is important if you create a 3D object from the curve (extrusion, revolution, or skinning).
NURBS curves should be drawn clockwise.
When you draw a Linear, Bezier, Cardinal or B-Spline curve, enter points counterclockwise. By doing this, the object's surface normals point in the correct direction and the object is rendered correctly.
If you draw a curve in the wrong direction, you can invert it using the Effect->Inverse or the Effect->Curve Controls command. i
You can edit the curve using the Edit menu cell commands starting on Edit->Move Point. To edit the curve resolution, or modify any clusters or shapes defined for the curve, you can use the Info->Selection command.
A Linear curve is made up of straight line segments that join all control points. It is used to create straight edges and should not be used when smooth curves are needed.
A Bezier curve passes through the control points. Each control point has a "handle" (tangent) which allows you to edit the curve's shape.
For information on editing Bezier curves, see the Modifying a Bezier Curve's Shape section of the Modelling User's Guide.
A B-Spline curve is made up of smooth arc segments. It does not pass through the control points. When you draw this curve, the first and last points are generated automatically.
A Cardinal curve is made up of smooth arc segments that pass through the control points. Like B-Splines, the first and last control points are automatically generated. This curve also has a tension on the control points that can be modified in the Curve Info dialogue box displayed by choosing the Info->Selection command.
NURBS stands for Non-Uniform Rational B-Splines, which are described in detail in Some Basics about NURBS Curves of the Modelling User's Guide.
When drawing a NURBS curve, you can choose its parameterization using the Draw->NURBS Curve Setup command. After drawing, you can use the Effect->Reparameterization command and dialogue box if you wish to change the curve's parameterization.
The Draw->Bezier Free Form command allows you to draw a curve freely as you drag the mouse. When you release the mouse button, the curve is optimized and converted to a Bezier curve. The points on a Bezier free form curve may be of different continuity (C0, C1, or G1) and thus the handles can be different colours.
Tip:
Work in the default window size. If you zoom in on the window, the detail of your curve might be lost.
The Draw->NURBS Free Form command allows you to draw a curve freely as you drag the mouse. When you release the mouse button, the curve is optimized and converted to a NURBS curve.
Tip:
Work in the default window size. If you zoom in on the window, the detail of your curve might be lost.
The Draw->NURBS Curve Setup command lets you indicate:
To modify curve parameterization, choose the Effect->Reparameterization command, which offers you the same choices of parameterization.
Type
Refers to the degree of curve you wish to draw. The degree of the curve determines the minimum number of points required to create an interpolated curve. It also affects the smoothness and continuity of the curve.
Note:
For explanations of terms related to NURBS, including degree and continuity, see the Some Basics about NURBS Curves section of the Modelling User's Guide.
- Linear creates a NURBS curve of the first degree and zero-order continuity (C0) You only need to draw two points to create an interpolated curve segment representing a straight line at any slope.
- Quadratic creates a NURBS curve of the second degree and first- order continuity (C1). You must draw at least three points to create an interpolated curve.
- Cubic creates a NURBS curve of the third degree and second-order continuity (C2). You must draw at least four control points to get an interpolated curve.
Parameterization
- Non-Uniform: The first time the curve is drawn, the delta between successive knots is related to the distance between successive control points.
The parameterization is not recomputed when you change the geometry of the curve (by moving, adding or deleting points). For this reason, the effect of changes are more localized if you use non-uniform parameterization than if you use chord length and centripetal. See also Uniform parameterization.
Non-uniform is the default value used for drawing a NURBS curve in SOFTIMAGE 3D.- Chord Length: The delta between successive knots is related to the actual length of the curve segment, which in turn is approximated to the distance between control points.
- The parameterization is completely recomputed when you change the curve geometry.
- Centripetal: The delta between successive knots is related to the square root of the length of the curve segment. This tends to make smoother curves (in some cases), but usually distorts texture mapping on surfaces.
- The parameterization is completely recomputed when you change the curve geometry.
- Uniform: The delta between successive control points is expressed in equal increments of 1, with no regard to the actual length of the curve segment. This choice may seem paradoxical, but just as whole numbers are a subset of the real number set, uniform parameterization can be seen as a subset of the generalized set of "non-uniform."
Note:
The effect of changes are more localized if you use Uniform or Non-uniform parameterization than if you use Chord Length and Centripetal.
Data Fitting
These parameters are only relevant to these two operations in which curves are fitted to sampling data: projecting curves and extracting curves.
Note:
These are global parameters. If you set them for an extracted NURBS curve, they are still in effect for your next projected or trim curve.
This slider lets you select how closely you wish the resulting curve to fit the input data.
By default, error tolerance is set low. When speed is more important than precision, as when working on a large project, you may wish to set it higher.
Sets the angle at which the sharp angles in the input data remain sharp or discontinuous in the resulting curve, and no rounding takes place. The default value is 60 degrees.
This means that angles greater than 60 degrees still receive some rounding. Angles less than 60 degrees would remain sharp (even if the curve is of quadratic or cubic degree).
If you set an angle of 5 degrees, a peak would have to be very sharp to make a discontinuous point. Otherwise, there is some rounding.
The Draw->Border command in the Model module allows you to create borders around curves or faces. This tool is useful for creating mattes. Simply specify the width of the border to create a new curve with edges parallel to those of the original.
The Draw->HrcBorder command in the Model module lets you create borders around hierarchies of curves or faces. The Path->AnimatedBorder and Path->HrcAnimatedBorder commands in the Motion module are animated versions of this effect.
For the Border effect to work properly, all the control points of the curve or face must lie in a single plane; however, the plane does not have to be restricted to the orthogonal axes (xy, yz, or xz).
The border is created.
Distance of Border
Allows you to define the width of the border. You can specify the distance from the curve in positive or negative values (distance is measured in SOFTIMAGE units). If using negative values, make sure that the value is not so large as to cause the curve or face to disappear completely.
Linearize Spline
When this option is selected, the curve (spline) is automatically linearized. It is usually necessary to linearize to obtain an accurate border. When using NURBS curves, the AnimatedBorder and HrcAnimatedBorder effects always assume that this option is active.
Step Size
When linearizing a curve, this step size is used rather than the one assigned to the curve, except in the case of a NURBS curve where the step size is always taken from the curve itself.
Preserve Number of Points
The Preserve number of points option ensures that the final point count is the same as the original count. When applying a border to non-convex shapes such as Bezier fonts, some points may be deleted to achieve the expected result. This is useful when performing additional operations, such as skinning, that require all elements to have the same number of points.
Thorough Checking
If using complex curves that are not providing the expected results, select this option to compute the geometry more thoroughly.
Note:
If this option is selected, the computation takes longer.
The Draw->HrcBorder command in the Model module allows you to apply the Border effect to a hierarchy of curves or faces in a single step.
The Draw->Border command in the Model module lets you create borders around a single curve or face. The Path->AnimatedBorder and Path->HrcAnimatedBorder commands in the Motion module are animated versions of this effect.
For the HrcBorder effect to work properly, all the control points of the curve or face must lie in a single plane; however, the plane does not have to be restricted to the orthogonal axes (xy, yz, or xz).
The border is created.
For a definition of the parameters, see the Border section.
The Draw->Curve->Pipe command in the Model module is a simple effect for bordering an open curve by a given amount and joining it with the original curve to create a new, closed curve. This is useful for quickly creating outlines of uniform width for walls or letters.
Pipe Width
The thickness of the offset.
Round Corners
When this option is active, it creates soft curve corners based on the Radius option. When inactive, it creates a hard cap at the corners of the new curve.
- Radius: Radius of corners if the Round Corners option is selected.
- Step: Number of steps in the corner curve if the Round Corners option is selected.
The Draw->Resample command in the Model module allows you to create new curves based on an existing curve. You select a curve and the desired number of samples; a new curve is then created with the corresponding number of control points and the same shape as the original curve. Resample is typically used when you need several curves with the same number of control points, such as when skinning.
The Path->AnimatedResample command in the Motion module is the animated version of this effect.
A new curve is created.
Number of Samples
Allows you to specify the number of control points that the resulting curve will have.
Resulting Spline
Allows you to select the resulting curve (spline) type: Linear,
B-Spline, or Cardinal.
Step
Sets the SOFTIMAGE 3D Step parameter for the result if the selected curve type is B-Spline or Cardinal.
Last updated 08-apr-1998