An interpolation curve consists of a curve that interpolates or approximates a sequence of points. To create an interpolation curve, in the Geometry toolbar, from the More Primitives (3D or 2D ) menu, select Interpolation Curve (). You can also right-click the Geometry node to add this node from the context menu. It is also possible to create an interpolation curve interactively by choose Interpolation Points () or Start, Tangent, Other () from the Interpolation Curve menu on the Sketch toolbar.

From the Type list, select Solid, Closed curve, or Open curve to specify if the interpolation curve is a solid object (only available in 2D) or a closed or open curve object. If Solid or Closed curve is selected, a point is automatically added if needed to close the curve, and the curve has continuous first and second derivatives everywhere.

From the Data source list, select Table to specify the points to interpolate in a table in the Settings window. This is the default data source. You can move rows up and down in the table, remove a row from the table, and clear the table using the buttons underneath the table. You can also load table data from file and save the table data to a file.

From the Data source list, select Vectors to specify the points to interpolate as vectors (lists) in the fields x, y, and (3D only) z; r and z in 2D axial symmetry; xw and yw in work planes. Each field can contain a list of numbers or expressions containing parameters, separated with commas or spaces. Click the Range button () to use the Range dialog box for specifying the vector of values for each coordinate.

From the Data source list, select File to read the points to interpolate from a text file. Specify the filename in the Filename field or click the Browse button. If Data format is Spreadsheet, the file must be a text file with the number of columns equal to the dimension of the geometry sequence, and one row for each data point. The columns can be separated by a space, tab, comma, or semicolon character. If Data format is Sectionwise, the file must be in the sectionwise COMSOL Multiphysics postprocessing data format (see About the Sectionwise Data Format for Data Export). The entries in the file should be numerical. In general, nonnumerical tokens and header lines are ignored. Click the Import to Table button to copy the file contents into the data point table and change the Data source to Table.

If Data source is File, changes in the file do not automatically cause the interpolation curve feature to be rebuilt. To rebuild the feature after a change in the file, click the Rebuild with Current File button.

In the Relative tolerance field, enter the maximum allowed distance between the generated curve and the sequence of points. The default value 0 implies that the curve interpolates all points. If the relative tolerance is larger than 0, the curve does not necessarily interpolate all points, but the first and last points are interpolated.

This section is visible only when the object type is Open curve and the Relative tolerance is 0. Also, this section is not visible if Data source is File ad Data format is Sectionwise.

From the Condition at starting point list, choose None (the default) to have no extra condition, choose Tangent direction to specify a tangent in the x, y, and z (3D) fields, or choose Zero curvature.

From the Condition at endpoint list, choose None (the default) to have no extra condition, choose Tangent direction to specify a tangent in the x, y, and z (3D) fields, or choose Zero curvature.

For the end conditions, the zero curvature is also called natural spline. The tangent direction is also called a clamped spline. Only the direction of the tangent vector matters; the magnitude is not used.

The coordinate system in which the curve coordinates above are interpreted. From the Work plane list, select xy-plane (the default, for a standard global Cartesian coordinate system) or select any work plane defined above this node in the geometry sequence. If you choose a work plane, the work plane and its coordinate system appear in the Graphics window, using an extra coordinate triad with the directions xw, yw, and zw (which are then used to specify the curve’s position).

Select the Resulting objects selection check box to create predefined selections (for all levels — objects, domains, boundaries, edges, and points — that are applicable) in subsequent nodes in the geometry sequence. To also make all or one of the types of resulting entities (domains, boundaries, edges, and points) that the interpolation curve consists of available as selections in all applicable selection lists (in physics and materials settings, for example), choose an option from the Show in physics (Show in instances if in a geometry part; Show in 3D in a plane geometry under a work plane in a 3D component) list: All levels, Domain selection, Boundary selection, Edge selection (3D only), or Point selection. The default is Domain selection, which is suitable for use with materials and physics defined in domains. For use with a boundary condition, for example, choose Boundary selection. These selections do not appear as separate selection nodes in the model tree. Select Off to not make any selection available outside of the geometry sequence. From the Color list, choose a color for highlighting the resulting objects selection. See Selection Colors.

If you want to make the resulting entities contribute to a cumulative selection, select a cumulative selection from the Contribute to list (the default, None, gives no contribution), or click the New button to create a new cumulative selection (see Cumulative Selections).