Offset Curve on Surface

https://github.com/nortikin/sverchok/assets/14288520/e884f6e8-d640-40b3-9ff0-f75f0aefc8a7

Functionality

This node does the following:

  • Takes a Surface and a Curve, which is supposed to be in UV space of the surface;

  • Draws a curve which is a result of mapping the provided curve into 3D space by the surface (similar to “Curve on Surface” node works);

  • Then offsets that curve by specified amount, while remaining within the surface.

In some simple cases, it is possible to perform similar offset operation by offsetting the original curve in surface’s UV space, and then mapping the result into 3D space. But as surface may stretch or compress it’s UV space in different proportions in different places, in any non-trivial case the result would be very imprecise. This node, on the other hand, guarantees that the distance between the original curve and it’s offset will be equal to specified amount with good precision.

Curve domain and parametrization: the same as of original curve.

Inputs

This node has the following inputs:

  • Curve. The curve (in surface’s UV space) to be offsetted. The curve is supposed to lie in XOY, XOZ or YOZ coordinate plane, depending on Curve Plane parameter. This input is mandatory.

  • Surface. The surface, in which the offset is to be performed. This input is mandatory.

  • Offset. Offset amount (offset distance in 3D space). The default value is 0.1. This input is available only when Offset type parameter is set to Constant.

  • OffsetCurve. The curve defining the offset amount for each point of original curve. The curve is supposed to lie in XOY coordinate plane. The node uses this curve’s mapping of T parameter to Y coordinate. For parameter of this offset curve, the node will use either parameter of the original curve, or it’s length share, depending on Offset curve type parameter. This input is available and mandatory only if Offset type parameter is set to Variable.

https://github.com/nortikin/sverchok/assets/14288520/163ec6cb-3a92-4665-83bd-77ff636fa747

Parameters

This node has the following parameters:

  • Curve plane. The coordinate plane where original curve is supposed to lie. The available values are XY, YZ and XZ. The default value is XY, which means that the original curve should lie in XOY coordinate plane, X coordinates of it’s points will be used as surface’s U parameter, and Y coordinates of curve’s points will be used as surface’s V parameter values.

  • Offset type. This defines how the offset amount is specified. The available values are:

    • Constant. The offset amount is constant and it is specified in the Offset input.

    • Variable. The offset amount is changing along the curve; the offset amount at each point of the original curve is defined by another curve, which is provided in OffsetCurve input.

    The default value is Constant.

  • Offset curve use. This parameter is available only when Offset type parameter is set to Variable. This defines what will be used as T parameter when calculating offset amount for each point of original curve. The available values are:

    https://github.com/nortikin/sverchok/assets/14288520/e5785039-52e5-481e-aea7-b3becee9d4f4

    • Curve parameter. T parameter of the original curve will be used. Note that in some cases this will distort the “offset curve” (compress it in one places and stretch in other places), as curve length is not required to be proportional to it’s parameter.

    • Curve length. Length of corresponding segment of original curve will be used. This allows more precise control over where the offset amount should change. But this option is slower.

    The default option is Curve parameter.

  • Length resolution. This parameter is available only when Offset type parameter is set to Variable, and Offset curve use parameter is set to Curve length. This defines the resolution for curve length calculation. The bigger the value, the more precise the calculation will be, but the slower. The default value is 50.

    https://github.com/nortikin/sverchok/assets/14288520/56e9511a-bd1a-4899-bd85-734a3a69429a

Outputs

This node has the following outputs:

  • Curve. The offsetted curve (in 3D space).

  • UVCurve. The offsetted curve in surface’s UV space; it will lie in XOY, YOZ or XOZ coordinate plane, depending on Curve plane parameter.

Examples of usage

Constant offset of a curve on a surface:

https://user-images.githubusercontent.com/284644/85555664-922f7500-b63f-11ea-8479-9ee8db89ee11.png

Similar setup, but with variable offset amount, controlled by a curve from “Curve mapper” node:

https://user-images.githubusercontent.com/284644/85555750-a8d5cc00-b63f-11ea-8f28-3565e3a8d1e4.png