How can you make an open curve follow the the topology of a surface?

example file.3dm (118.8 KB)

in this example, if I start to draw in the perspective view, I don’t have much control of the line besides osnaps, meanwhile in other views, the line will follow the axis, and not the surface topology itself

on suites like maya or blender, there’s a tool called cut/knife tool, that kinda does what I want to do,

To create a curve on a surface:

Rhino command: InterpCrv Rhinoceros Help - InterpCrvOnSrf | Rhino 3-D modeling (mcneel.com)

Free plugin from McNeel: CurveOnSurface CurveOnSurface | Food4Rhino

Osnaps for selecting points on surface and polysurfaces: OnSrf, POnSrf, OnPSrf, POnPSrf
Rhinoceros Help (Scroll down to the Object snaps on an object section)

OnSurface (OnSrf)

Snap to and track over a surface for one pick.

OnSurface example

Place a point object on a surface.

OnSurface steps

  1. Select the surface.
    The marker moves only over the surface.
  2. Click the left mouse button to place the point.
    If you are tracking over a polysurface, the marker is restricted to the single selected face. The cursor changes shape to indicate that you cannot pick. To track over the whole polysurface, see the OnPolysrf object snap.

To access this object snap on the Osnap control

  • Press and hold the Ctrl key and hover the mouse over the Osnap control.

PersistentOnSurface (POnSrf)

Snap to and track over a surface until the command completes.

To access this object snap on the Osnap control

  • Press and hold the Ctrl key and hover the mouse over the Osnap control.

Percentage (Percent)

The selected curve is marked with temporary black points that can be snapped when the Point object snap is disabled.

If the percentage is less than 50, the curve is marked with multiple snap points. For example, when using 30, you get snap points at 30%, 60% and 90%.

To access this object snap on the Osnap control

  • Press and hold the Shift key and hover the mouse over the Osnap control.

OnPolysurface (OnPSrf)

Snap to and track over a polysurface for one pick.

OnPolysurface example

Place a point object on a polysurface.

OnPolysurface steps

  1. Select the polysurface.
    The marker moves only over the polysurface.
  2. Click the left mouse button to place the points.

To access this object snap on the Osnap control

  • Press and hold the Ctrl key and hover the mouse over the Osnap control.

PersistentOnPolysurface (POnPSrf)

Snap to and track over a polysurface until the command completes.

To access this object snap on the Osnap control

  • Press and hold the Ctrl key and hover the mouse over the Osnap control.

If you want to work on plane you can create a custom CPlane. Rhinoceros Help - CPlane | Rhino 3-D modeling (mcneel.com)

Hello David,

Thank you for listing all of these related tools. It’s quite helpful to have them all in one place.

Andy