In brief
- Flow realigns objects or groups from a base curve to a target curve.
- FlowAlongSrf maps objects from a base surface to a target surface.
- Balanced surface parameterization in FlowAlongSrf helps prevent noticeable stretching.
- With Rigid enabled, objects move without deforming; when disabled, their shape may change to match the target geometry.
What will you learn in this guide?
The Flow and FlowAlongSrf commands in Rhino 8 transfer objects from base geometry to target geometry. Flow works between curves, while FlowAlongSrf maps between surfaces. This guide covers the steps for using both commands, the options that affect the transformation, and issues you may encounter in the result.
Placing repeated elements along a curved path in an architectural model, or moving an object layout from one surface to another, are examples that illustrate how these commands work. They do not guarantee a particular project outcome: the direction and shape of the mapping depend on the selected base and target geometry and the chosen options.
Requirements and preparation
The sources are the Rhino 8 help documents for Flow and FlowAlongSrf. They do not specify a separate account requirement or additional software for these commands. The option names and usage information here are based on the Rhino 8 documentation.
Before you begin, identify the objects to transform and the geometry to use for mapping. Flow requires a base curve and a target curve; FlowAlongSrf requires a base surface and a target surface. This geometry determines where the command starts and the shape into which the objects are mapped.
Surface parameterization is particularly important in FlowAlongSrf. McNeel’s documentation notes that balanced parameterization of the base and target surfaces helps prevent noticeable stretching in the objects. So pay attention not only to the appearance of the surfaces, but also to how they are parameterized during mapping.
1. Move objects along a curve with Flow
Flow realigns objects or groups of objects from a base curve to a target curve. It can be used to map a straight shape onto a curved one. Creating the shape first in a straight, regular form may be easier than modeling it from the outset around a complex curve.
Select the objects to transform. Identify the objects or groups to map along the curve.
Run the Flow command. Rhino Help lists the command under Transform > Flow along Curve.
Select the base curve near one of its ends. The selection should be close to the curve’s start or end point.
Select the target curve near the corresponding end. Selecting corresponding ends on the two curves determines the mapping direction.
Review the deformation and direction options. Use the Rigid option depending on whether you want the objects simply moved or reshaped to follow the target curve.
When Rigid is enabled, objects are only repositioned along the target curve; when disabled, they deform as they move. RigidGroups determines whether groups are kept rigid together or individually when Rigid is enabled. Use this option to control group behavior.
Stretch determines whether objects are stretched or compressed along the curve and whether the relationship between the base curve and target curve is preserved. With Local, the area of influence around the base curve can be defined like a tube: objects inside the tube flow, those outside remain fixed, and the effect diminishes at the tube wall.
The TargetSurface option can provide additional direction information for the target curve. It maps the “up” direction of objects relative to the normal of the target surface. If objects are directed to the unwanted side of the surface, the source recommends using the Flip or Dir commands to change the direction of the target surface normal.
For 3D target curves, Roadlike uses frames made up of axes to calculate rotation. When the option is enabled, the starting point and direction of the road-like axis are specified on the base curve and target curve. Pressing Enter while choosing the direction, or selecting Automatic, uses the CPlane-Z axis of the viewport.
2. Map objects to a surface with FlowAlongSrf
FlowAlongSrf maps objects by transforming them from a base surface to a target surface. Rhino Help lists the command under Transform > Flow along Surface.
Identify the base and target surfaces. The surface associated with the objects’ current layout is the base; the surface defining the form to map to is the target.
Start the command and select the base surface. Pick an edge near one of the base surface’s corners.
Select the corresponding edge on the target surface. Make this selection on the side corresponding to the corner on the base surface.
Check the Rigid and RigidGroups options. Rigid determines whether objects are only moved or deformed as they move. When Rigid is enabled, RigidGroups handles groups together or individually.
Review the AutoAdjust state and mapping direction. With AutoAdjust enabled, UV directions are not used; the corner and edge near the selected location define the start point and U direction, with the other direction becoming V. The N direction is determined from the UV directions using the right-hand rule.
When AutoAdjust is enabled, selecting non-matching points on the base and target surfaces can cause the object to map to the opposite side of the target surface. This warning applies when AutoAdjust is enabled. When the option is off, the command uses the UV directions of the base and target surfaces, and the selection locations are not critical. With the option off, the N direction is still determined from the UV directions using the right-hand rule.
If one of the surfaces is trimmed, the surface region used for mapping also changes depending on the AutoAdjust state. When the option is enabled, the trimmed surface’s shrunk version is used; when it is disabled, the underlying surface is used. This is one of the points to check when investigating an unexpected mapping direction or placement.
PreserveStructure determines whether the control point structure of a curve or surface is retained after deformation. If the structure is preserved, too few control points in the object may reduce deformation accuracy. When preservation is disabled, the geometry can be rebuilt as needed for a more accurate deformation. This option does not apply to polysurface objects and is not shown when only a polysurface is selected.
Common issues and next steps
Objects map in an unexpected direction: Check whether you selected corresponding ends on the base and target curves, or edges near corresponding corners on the surfaces. For FlowAlongSrf, also check the AutoAdjust state and UV directions.
FlowAlongSrf stretches objects: Review the surface parameterization. McNeel notes that unbalanced parameterization can cause stretching; a rebuilt target surface with more closely spaced isocurves may help achieve balanced parameterization.
Objects change shape: Check the Rigid option. When enabled, objects are only moved; when disabled, they deform to match the target geometry.
Preserving structure does not make deformation more accurate: There may be too few control points when PreserveStructure is enabled. Disabling structure preservation allows the command to rebuild the geometry as needed.
As a next step, try the commands on simple geometry that is easy to evaluate. Testing how the selection points, Rigid state, and surface parameterization affect the result separately makes it easier to troubleshoot issues in a project model.
In architecture, interior design, and archviz workflows, Flow can be used for object layouts to be mapped along a curved path, while FlowAlongSrf can be considered for layouts moved between surfaces. In particular, preparing repeated elements on regular base geometry and mapping them to the target form can make the modeling approach more systematic. However, any changes in shape to façade or interior elements should be checked carefully. The documentation does not provide information about hardware requirements, licensing costs, or compatibility with other software; these should be verified separately for the installation in use.
Sources and licensing
This guide has been adapted into Turkish from McNeel’s Rhino 8 help documents for Flow and FlowAlongSrf. Both sources are provided under a free-use label.
Sources
2 sourcesSource texts are not republished; short quotes are marked, everything else is our own summary and commentary.
For architecture and visualization teams in Turkey, Flow and FlowAlongSrf offer a way to set up repeated elements on regular base geometry before adapting them to a curve or surface. Being able to distinguish, through the options, which elements are moved and which are deformed is particularly useful for formal explorations.
However, checking the result should be part of the workflow: surface parameterization, selection direction, and the Rigid setting all affect the output. Since the documentation does not specify hardware or licensing costs, it would not be appropriate to make assumptions on these points. Offices should try the commands in their own modeling workflows and inspect critical geometry closely.
Frequently asked questions
What is the difference between Flow and FlowAlongSrf in Rhino?
Flow realigns objects or groups from a base curve to a target curve. FlowAlongSrf maps objects from a base surface to a target surface.
Why does FlowAlongSrf stretch objects?
According to McNeel’s documentation, unbalanced surface parameterization can cause objects to stretch. Balanced parameterization helps prevent noticeable distortion.
What changes when AutoAdjust is off in FlowAlongSrf?
The command uses the UV directions of the base and target surfaces; the selection point locations are not critical. For trimmed surfaces, the underlying surface is used for mapping.
