Move NURBS Curve Point

Functionality

This node suggests several ways of adjusting a NURBS curve so that it would go through another point at specified position, while keeping most of the curve more or less in place.

Different methods of curve adjustment allow different degrees of freedom in specifying what do you want to move and where to.

Inputs

This node has the following inputs:

• Curve. The NURBS Curve object to be adjusted. This input is mandatory.

• T. The value of curve parameter, point at which is to be moved. The default value is 0.5.

• Index. This input has different meaning for different curve adjustment methods being used:

  • For Move one control point method, this is the index of curve control point to be moved.

  • For Adjust one weight method, this is the index of curve weight to be adjusted.

  • For Adjust two weights method, this is the index of first of two curve weights to be adjusted. The second weight adjusted will be the following one.

  • For other methods, this input is not available.

  The default value is 1.

• Distance. The distance for which curve point at T parameter is to be moved.

  • For Adjust one weight method, positive values mean move the point toward corresponding control point (index of which is defined in Index input). Negative values mean movement in the oppposite direction.

  • For Adjust two weight method, positive values mean move the span of curve towards the corresponding curve control polygon leg (the one between control points Index and Index+1). Negative values mean movement in the opposite direction.

  • For other methods, this input is not available.

  The default value is 1.0.

• Vector / Point. This input is available only when Method is set to Move one control point, Move control points, or Insert knot. If Mode parameter is set to Relative, this input specifies the vector for which the curve point at T parameter is to be moved. In Absolute mode, this input specifies the point where curve point is to be moved to. The default value is (1.0, 0.0, 0.0).

Parameters

This node has the following parameters:

• Method. The method to be used to adjust the curve. The following methods are available:

  • Move one control point. The node will move exactly one control point of the curve, to move curve point at T parameter by Vector. The index of control point being moved is specified in the Index input. Note that it is not always possible to move arbitrary curve point by arbitrary vector by moving specified control point. In intuitive terms, the point to be moved has to be near control point being moved.

  • Adjust one weight. The node will adjust one weight of the curve, to move curve point at T parameter directly towards corresponding control point, or in the opposite direction. The index of the weight being adjusted (and the index of corresponding control point) is specified in the Index input. Movement distance is specified in the Distance input. Note that it is not always possible to move arbitrary curve point by adjusting the specified curve weight. Also, if you try to move the point too far with this method, you will probably get unexpected curve shapes.

  • Adjust two weights. The node will adjust two weights of the curve, to move curve point at T parameter, together with neighbouring curve span, towards the corresponding control polygon leg, or in the opposite direction. The index of the first weight to be adjusted (and corresponding control point index) is specified in the Index input. Note that it is not always possible to move an arbitrary curve point by adjusting the specified weights. Also, if you try to move the point too far with this method, you will probably get unexpected curve shapes.

  • Move control points. The node will move several control points of the curve (approximately p of them, where p is the degree of the curve), to move curve point at T parameter by the specified vector. The node will automatically figure out which control points have to be moved. This algorithms gives most smooth results, but it requires more computations, so it is probably less performant.

  • Insert knot. The node will insert additional knot into curve’s knotvector, and then move three control points, in order to move curve point at T parameter by specified vector. The node will automatically figure out which control points have to be moved.

  The default option is Move one control point.

• Preserve tangent. This parameter is available only when Method is set to Move control points. If checked, the node will try to preserve the direction of curve tangent at the point being moved. In many cases, this gives only a slight difference; but sometimes this will make the result smoother. Unchecked by default.

• Mode. The available options are Relative and Absolute. In the Relative mode, you specify the movement vector; in the Absolute mode, you specify the target point. The default mode is Relative.

Outputs

This node has the following output:

• Curve. The adjusted curve.

Examples of Usage

An illustration of Move one control point method. Here, black is the original curve; dark blue is it’s control polygon; light blue point is the point at T parameter on the original curve. Green is the resulting curve, and big green point is the resulting point. In this case, only control point number 7 is moved.

An example of Adjust one weight method. Here, the blue point is moved towards the control point number 8. Curve control points are not moved, only one curve weight is changed.

An example of Adjust two weights method. Here, the blue point is pushed away from control polygon leg between control points 4 and 5 (note the negative value of Distance parameter). Again, control points are not moved, only weights are changed.

An example of Move control points method. Here, the blue point is moved by specified vector by moving of three control points (6, 7 and 8).

An example of Insert knot method. The point is moved by inserting a knot, thus creating additional control points, and moving three control points.