Fit surface node

Fits a spline curve to points, or a spline surface to a mesh of points.

All

Parameters

Example files

Any type of face or surface represents a valid input. The Fit op looks only at the control vertices (CVs) of the primitives, treating the CVs as data points to run the fit through. For example, if a cubic NURBS surface and a mesh have the same number of rows and columns and identical points, they will yield an identical fit because the Spline bases of the input NURBS surface are ignored.

The Fit op generates two types of outputs: primitives that roughly follow the path of the data points without necessarily going through the data points; and primitives that touch all the data points. The first type, known as “approximation”, is used primarily to extract a lean, smooth shape from a heavy data set, lending itself well to data reduction. The second type, known as “interpolation”, often serves as a smoothing tool for paths that must go through specified target positions.

Parameters

Fit

Method

Fitting style: by approximation or by interpolation.

Primitive Type

Type of output spline primitive: NURBS or Bezier.

Connectivity

Type of surface generated when input is a mesh:

Rows	Creates horizontal lines, which are display curves.
Column	Creates vertical lines, which are display curves.
Rows & Cols	Creates both rows and columns, all display curves.
Triangles	Builds the surface with triangles (not used).
Quadrilaterals	Creates four-sided quadrilaterals.
Alt. Triangles	Creates the surface with alt. triangles (not used).

U Order

Order of fitted spline in the U direction.

V Order

Order of fitted spline in the V direction.

Approximation

Tolerance	Primary precision factor in fitting.
Smoothness	Allows for more or less roundness in the shape.
U Multiple Knots	Enables preservation of sharp turns of the data in U.
V Multiple Knots	Enables preservation of sharp turns of the data in V.

Interpolation

Scope

Establishes the interpolation method:

Global	Yields as many CVs as data points.
Local	Yields more CVs than data points but the fit is tighter.
Breakpoints	Similar to Global, only the basis reflects data directly.

U Data Parameter

Specifies the data parameterization in the U direction:

Uniform	Uses evenly spaced parameter values.
Chord Length	Parameter values based on relative distances between data.
Centripetal	Similar to Chord Length, better suited for sharp corners.

V Data Parameter

Specifies the data parameterization in the V direction:

Uniform	Uses evenly spaced parameter values.
Chord Length	Parameter values based on relative distances between data.
Centripetal	Similar to Chord Length, better suited for sharp corners.

U Wrap

Optionally close the generated spline in the U direction.

V Wrap

Optionally close the generated spline in the V direction.

Fit Corners

Enables corner preservation if the scope is Local.

Example files

FitCurves

$HFS/houdini/help/examples/nodes/sop/fit/FitCurves.cmd

Load | Launch

This is an example of how to use the Fit SOP to fit a NURBs curve to a basic polygon curve.

Fitting builds a new NURBs or Bezier curve through the input geometry’s points.

There are two methods for doing this:

Interpolation fitting outputs the same number of cv’s as the input curve (Original Polygon Curve).

Approximation fitting reduces the number of cv’s, while approximating a curve through the input points.

Play the animation to see how these two methods affect the resultant curve over time.

FitSurfaces

$HFS/houdini/help/examples/nodes/sop/fit/FitSurfaces.cmd

Load | Launch

This contains examples of fitting a Polygon Mesh to a NURBS surface through the use of the Fit SOP. There are two methods of fitting:

Approximation, which generates primitives that roughly follow the path of the data points.
Interpolation, which generates primitives that touch all the data points.

Usages in other examples

Example name	Example for
Add	Add surface node	Load \| Launch