Creating Curved Surfaces with Patch in Rhino 8: A Step-by-Step Guide

What will you learn in this guide?

This walkthrough covers the workflow for creating curves in Rhino 8 and using the Patch command to generate a surface from them. You’ll learn the key differences between Curve and InterpCrv, which inputs Patch accepts, and which options affect the surface result. The aim isn’t to provide a formula that guarantees the same result for every model, but to show how to evaluate options with small tests and create a suitable surface.

Patch fits a surface to selected curves, meshes, point objects and point clouds. However, it isn’t guaranteed to pass exactly through every input curve. That’s why it’s important to prepare clear boundary and shaping curves first, then review the preview and adjust the settings.

Requirements

• The Curve, InterpCrv and Patch commands described in McNeel’s Rhino 8 documentation.

• Curves, meshes, point objects or point clouds to use as Patch inputs. This guide focuses on a curve-based example workflow.

• A surface resembling the target shape, if you want to use a starting surface. This option is not required.

The source documentation does not specify account requirements. No specific hardware, account type or additional software is required for this guide either. The official Rhino 8 documentation is the reference for the appearance and details of the command options.

Step-by-step: prepare curves and create a surface

1. Decide how to create the curve

Use the Curve command to shape a curve with control points, or InterpCrv to draw a curve that passes through the locations you select. The two commands behave differently: with Curve, control points define the curve’s shape; InterpCrv passes through the selected locations.

In InterpCrv, the Degree setting determines the desired curve degree. According to the documentation, the command uses the requested degree even if you select only the start and end points. With Curve, the result may not have the requested degree if there aren’t enough control points. Using a value other than the degree switches SubDFriendly to No; SubDFriendly is compatible only with degree 3.

2. Complete the curves correctly

If you need a boundary curve, consider the closing options in the Curve or InterpCrv command. Close closes the curve smoothly and periodically; Sharp creates a non-periodic closure with a kink at the join. AutoClose helps close the curve when the cursor nears the start point. As the commands don’t have identical options, check the command line to confirm which setting you’re using.

Knots options may matter in InterpCrv when the spacing between points varies significantly. Chord uses the distance between selected points; SqrtChrd uses the square root of that distance to determine spacing. If the points are spaced approximately evenly, you can use Uniform. When the selected points are evenly spaced along the entire curve, all three options create the same curve.

3. Select the Patch inputs

Start the Patch command and select the curves, meshes, point objects or point clouds that the surface will be based on. If you want a trimmed Patch, the boundary curves must form a closed shape, and adjoining curves must be selected in sequence. This ensures that each new curve connects to one selected previously.

You can also select additional curves to shape features such as a dip or peak in the middle of the surface. These shaping curves don’t need to be connected to each other. Keeping boundary curves distinct from additional curves that influence the surface shape helps organize your selection.

4. Adjust the Patch options

Sample point spacing sets the physical distance between sample points along an input curve. According to the documentation, each curve requires at least eight sample points. Surface U spans and Surface V spans set the number of spans in the U and V directions of the automatically created surface; these values are also used when the starting surface is a 1x1 span plane.

Stiffness affects how much the best-fit plane deforms to the selected points and the points sampled along the curves. As the value increases, the surface becomes stiffer, more rectangular and more planar. McNeel notes that you can try small or very large values, including values above 1000. This doesn’t mean that a high value is right for every job; check the result against the target shape.

5. Consider the starting surface and edge options

If you have a surface that resembles the target shape, you can select it with Select starting surface. Starting surface pull affects how closely the resulting surface stays to the starting surface; higher values make the resulting surface more closely follow the starting shape. Preserve edges keeps the edges of the starting surface in place. Use this option when deforming a surface with curves or points while keeping its existing edges from moving.

Adjust tangency is intended to match the tangent direction when the input curves are edges of existing surfaces. Automatic trim attempts to find the outer boundary and trim the surface. Check the effects of these options in the preview, especially when working with multiple curves.

6. Refresh the preview and assess the result

Use Preview to check the surface. After changing any setting, update the preview again; the previous view may not reflect the new options. The result may not pass exactly through each input curve. So look not only at whether the boundary closes, but also at the overall surface shape and how closely it follows the starting surface.

Common mistakes

Selecting the curves that define a closed Patch boundary in a random order disrupts the required sequence of adjoining curves. If you want a trimmed surface, make sure the curves form a closed shape and are selected in order. Also, additional curves that influence the shape don’t have to connect to one another; don’t confuse them with boundary curves.

Another common mistake is assuming that Patch will pass exactly through every input curve. The official documentation says this isn’t guaranteed. Increasing Stiffness also makes the surface stiffer and more planar, so don’t assume that simply raising the value will produce the desired curvature. Change the setting, refresh Preview and compare the results.

Treating Curve and InterpCrv as interchangeable can also affect the result. Curve works with control points, while InterpCrv passes through the selected locations. In InterpCrv, the StartTangent and EndTangent options don’t work when the degree isn’t 3 or when SubDFriendly=Yes. If you need to control tangency at the ends, review the curve settings accordingly.

Use in architectural and visualization workflows

Patch is an option for architects and 3D modeling professionals who want to create freeform surfaces from curves, points or existing surface data. It can be useful when exploring options for creating an initial surface that describes a shape with curves. However, the sources don’t specify a particular architectural use case or compatibility with visualization software, so compatibility of the Patch output with the next stage of your workflow should be verified separately.

If the surface result isn’t what you expect, McNeel recommends trying the Sweep2 command instead of Patch. If you select a starting surface and check Delete input, History won’t be saved. Keep this behavior in mind when modeling from an existing surface.

Next steps

First, try several Stiffness and span values with the same inputs, refreshing the preview after every change. Then, when using a starting surface, examine how Starting surface pull and Preserve edges affect the shape. Consider whether it’s better to work with control points or with a curve that passes through selected points. If Patch doesn’t produce a satisfactory result, compare it with Sweep2 as well.

Sources and license

This guide is a Turkish adaptation of McNeel’s official documentation for the Patch, Curve and InterpCrv commands in Rhino 8. The source records present these documents as freely licensed; the source pages do not specify a license name.