Creating Section Curves with Rhino 8’s Contour and Section Commands

This guide explains how to create section output from model geometry with the Contour and Section commands, as described in McNeel’s Rhino 8 help documentation. Contour cuts objects with evenly spaced planes to produce a series of results, while Section extracts the intersection with one defined plane. The commands are available under Curve From Objects > Contour and Curve From Objects > Section. The steps below are based on the options documented for Rhino 8; the documentation does not specify a recommended section spacing for any particular project.

When to use Contour and Section

Contour can be used when you need repeated sections or slices through a model. You define a starting point, the direction in which the planes advance, and the distance between contours. Planes can be generated in both directions from the starting point. This lets you obtain intersection results from multiple planes aligned along the same direction in a single operation.

Section is intended for creating a single section at a specific location. The cutting plane is defined by two points and is perpendicular to the current CPlane. So before running the command, consider where the section plane should pass and how it should be oriented. If you do not need a series of sections, Section offers a more direct approach.

Both commands can create curves or points where the cutting planes intersect objects. Hatch output, however, is not available in every case: it is created only for closed sections and when the object’s section style properties allow it. This means you should clarify both which command to use and what output you expect before starting.

Creating regularly spaced sections with Contour

1. Select the objects. Select the geometry to contour, then start the Curve From Objects > Contour command. The operation creates results where the cutting planes intersect the selected objects.

2. Set the starting point. This point defines the reference position for the contour planes. Planes can be created in both directions from here, so the starting position affects which areas the resulting slices cover.

3. Choose the direction perpendicular to the planes. This direction determines the orientation of the contour planes. According to the Rhino 8 documentation, the planes are perpendicular to the selected direction and the current CPlane. If the sections appear in an unexpected direction, check the CPlane and selected direction before running the command.

4. Enter the distance between contours. This value sets the spacing between adjacent cutting planes. The documentation does not provide a preset value or a recommendation that applies to all models, so choose the spacing based on the model’s scale and the required section density.

5. Adjust the range and output. Range defines the limits within which contours are created. Under Output, All allows curve, point, or hatch output; CurvesOnly excludes hatches and produces curves or points.

6. Choose properties and grouping. With AssignProperties, ByCurrentLayer creates output using the current layer and its properties, while ByInputObject uses the input objects’ properties. GroupObjectsByContourPlane groups objects created on the same contour plane. These settings help organize large numbers of section results in a file.

Whether the spacing is too tight or too wide depends on the project; the official documentation does not give a numerical threshold. Rather than assuming an exact number of curves in advance, a safer workflow is to run a small test and check that the contours cover the intended area and face the right direction.

Extracting a single section with Section

1. Select the objects to cut and open the command. Use Curve From Objects > Section. The command creates planar results where the objects intersect the defined cutting plane.

2. Define the plane with two points. Select the first point, then the second. These points are used to define the position and orientation of the section plane. The plane is perpendicular to the current CPlane, so check the working plane before proceeding.

3. Consider the plane’s extent. ExtendSection determines whether the section plane extends beyond the points you selected. If the section needs to cover the entire target objects, check this option; if the extent is unexpected, review the point selections and the option’s state.

4. Set the output type and properties. Output options control whether curves, points, or, when conditions allow, hatches are created. CurvesOnly does not create hatches. With AssignProperties, you can choose whether the output uses the current layer’s properties (ByCurrentLayer) or those of the input objects (ByInputObject).

5. Set up grouping. GroupObjectsBySectionPlane groups objects created from the same section plane. If the file contains results from different planes, this option can make it easier to manage each set separately.

The Range option documented for Contour is not among the options for Section. The Section documentation describes ExtendSection for controlling the plane’s extent, so avoid confusing the settings for the two commands.

Using the commands in architectural and visualization workflows

Contour can be used when you need regularly spaced section curves from an architectural model or slices across multiple planes. Section is a good choice when you need the lines and points produced by a single section plane. Rhino’s capabilities also include creating sections and contours on NURBS surfaces and meshes; the resulting geometry can be used in subsequent drawing or model-editing steps.

In your workflow, first decide which geometry to cut, then define the plane direction and expected output type. Choosing in advance whether to use the input objects’ layer properties or the current layer’s properties can reduce the need to reorganize the output later. When working with multiple section planes, grouping options also help you select and manage results together.

If you expect hatches, selecting All as the output may not be enough. Hatches are created only for closed sections and when the source object’s section style properties allow them. No hatch is created when the object’s section style is set to By Clipping Plane. In that case, check both whether the section is closed and whether this property is set as expected before evaluating the results.

McNeel’s documentation for these commands does not specify a recommended contour spacing, price, or particular hardware requirements. When setting an office standard, avoid presenting numerical values not found in the documentation as general Rhino recommendations. It is best to test the commands in the project file to verify direction and output type, and to assess software version, hardware, and licensing decisions separately based on the office’s own setup and purchasing information.

Common mistakes

• Using Contour when you need a single section: Contour is suited to a series of regularly spaced planes; Section is suited to a single section.

• Overlooking the CPlane: In both commands, planes are perpendicular to the current CPlane. If the direction is unexpected, check the CPlane and point selections.

• Assuming a missing hatch means the command has failed: Hatches are created only for closed sections and when the section style conditions allow them; they are not created when the setting is By Clipping Plane.

• Looking for Range in Section: This option is documented for Contour; the extent option documented for Section is ExtendSection.

• Leaving output organization until later: Decide on layer assignment and grouping by plane before creating the results.