How to Use Sample Curve and Trim Curve in Blender Geometry Nodes

What will you learn in this guide?

Sample Curve and Trim Curve in Blender Geometry Nodes complement each other, but serve different purposes when working with curves. Sample Curve reads data from a selected position along a curve. Trim Curve defines which section of a spline to use by removing parts from its start or end.

This guide covers how to set the sample position using a factor or distance, how to interpret Sample Curve’s outputs, and how to define a start-to-end range with Trim Curve. It also explains details that can affect the result when working with multiple splines, cyclic curves, and NURBS. The goal is not to provide a ready-made node setup, but to help you interpret the nodes’ inputs and outputs correctly.

Requirements

The official Blender manual used as the source is the Blender 5.2 LTS documentation. You’ll need Blender and Geometry Nodes; the sources do not specify any account, fee, special add-on, or hardware requirements. Check the available interface options against the version you’re using.

To follow along, you’ll need a curve component in Geometry Nodes and a basic understanding of how to build a node tree. No particular starter scene is required. Beginning with a simple curve containing a single spline makes it easier to isolate the effects of spline order and total length that can arise with multiple splines.

Step by step: Sampling curve data with Sample Curve

1. Connect the curve geometry. Connect geometry containing a curve component to the Curves input of the Sample Curve node. The node evaluates data at a selected point on the curve; it is not used to shorten the curve geometry.

2. Choose a sampling method. Factor sets the position as a proportion of the curve’s total length. Length specifies the distance to travel from the start. In other words, Factor defines a ratio, while Length defines a distance. Choose whichever makes the position easier to specify in your project.

3. Account for multiple splines. If the curve contains multiple splines, the position may be found using a cumulative total that also accounts for the lengths of preceding splines. Spline order corresponds to the order shown in the Spreadsheet Editor. You can use the Curve Index input to select specific splines; the index can be entered manually or taken from an Index Node. When All Curves is enabled, Curve Index is ignored, and the length calculation is based on the total length of all curves rather than the length within the selected curve.

4. Use the output you need. Position returns the location of the selected sample. Tangent is the normalized tangent direction at that point, while Normal provides the normalized curve normal. When a custom field is connected to the Value input, the Value output returns that field’s value at the sample position. At intermediate positions, the value is calculated from the available data of evaluated samples along the curve.

5. Use the direction data. The Tangent output can be used with an Align Rotation to Vector node to help align a rotation with the direction of the curve. Using the Normal output in a second alignment step provides direction information for another rotation axis. These outputs do not determine every placement decision in a scene on their own; the other connections in the node tree also affect the result.

Step by step: Shortening a curve with Trim Curve

1. Set the curve and selection. Connect the curve component to the Curve input of the Trim Curve node. The Selection input is a Boolean field that determines whether trimming is applied to each curve. This lets you choose which curves in the tree to trim.

2. Set the Start and End values. These inputs define the start and end points of the output spline. In Factor mode, they use proportions of each spline’s length and must be between 0 and 1. In Length mode, they specify distances from the start and must remain within the spline’s length.

3. Watch out for reversed ranges. If Start is greater than End, the result is a single point at the Start position, not a normal curve segment. If the output is unexpected, first check the selected mode, then check the order of the Start and End values.

4. Check the spline type and normals. Bezier splines remain Bezier in the output; the control structure at the ends is rearranged to create the trim boundaries while preserving the shape. NURBS splines are converted to poly splines as a result of the operation. Cyclic splines are not supported by Trim Curve. When the minimum twist method is used, trimming can affect the normals calculated from the final curve. The manual notes that in some cases, storing the original normals with Capture Attribute may help prevent this change.

Use in architecture and archviz workflows

In an architectural node tree, a curve might represent a circulation line, a path running along a facade, or a landscape boundary. Trim Curve can process a specific range of that path instead of using the entire curve. Sample Curve lets you use position and direction data from along the curve in subsequent operations. These features help you manage more explicitly which parts of a curve-based procedural tree to use and where to sample data from the curve.

With models containing multiple splines, it’s important to check spline order and total length calculations early. Sample Curve’s Curve Index and All Curves behavior can affect how a position is found. Starting with a single spline makes it easier to distinguish the effects of these options. The sources provide no information about hardware, licensing costs, or compatibility with other software; verify these separately before starting a project.

Common mistakes and next steps

It’s easy to confuse Factor with distance and Length with a ratio. Factor uses a ratio, while Length uses a distance measurement. With multiple splines, failing to account for total length and spline order can also make the sample position appear different from what you expected.

For Trim Curve, keep in mind that cyclic splines are not supported, NURBS splines are converted to poly splines, and a Start value greater than End produces a single point. For your first test, define a range on a single spline with Trim Curve, then inspect the Sample Curve outputs. Next, try multiple splines and evaluate Curve Index and All Curves separately. This makes it easier to determine whether an issue comes from the measurement method, spline order, or range values.

Sources and license

This guide has been adapted into Turkish based on the Geometry Nodes curve node documentation in the Blender manual. The Blender 5.2 LTS manual pages used are licensed under CC BY-SA 4.0.