Spline CV

The splinecv command draws a cubic B-spline by placing control vertices (CVs). The resulting curve is attracted toward each CV but does not pass through them — except at the very first and last vertex, where clamped knots anchor the curve exactly. This gives you intuitive shape control: pull a vertex to push the curve toward it without forcing it to touch every point.

Drawing a spline by control vertices

1. Type splinecv in the terminal or click the Spline CV toolbar button.
2. Click to place control vertices — each click adds a vertex. Or type X,Y and press Enter for an exact coordinate.
3. Press Enter to finish (at least 2 vertices required).

  CV ●         ● CV
      \       /
       \     /    ← curve pulled toward CVs
        \   /         but not passing through them
  CV ●   ●   ● CV (start/end: curve touches here)

The live preview updates as you move the cursor after each vertex, showing how the spline will look with the next point at the cursor position. Press Escape to discard all placed vertices and exit.

Coordinate entry

Instead of clicking, type an exact position for any control vertex:

1. Type the X value.
2. Press , — the terminal shows [X], [Y{cursor}].
3. Type the Y value.
4. Press Enter to place the vertex.

Keyboard reference

Key	Action
0–9, ., -	Start X coordinate entry
,	Lock X and move to Y entry
Backspace	Delete last typed character
Enter	Confirm typed coordinate, or finish the spline if no input is in progress and ≥ 2 vertices exist
Escape	Discard all vertices and exit

Grip editing — reshaping via control vertices

A selected CV spline exposes one grip per control vertex:

Grip	Position	What it does
Control vertex	At each CV position	Drag to move that CV — the curve reshapes toward the new position

There is no "move whole spline" grip. To translate the entire spline, use the Move command.

Selecting CV splines

Method	Behaviour
Click	Selects if the click lands near any point on the curve
Drag right (strict)	All sample points along the curve must lie inside the selection box
Drag left (crossing)	Any part of the curve that crosses the selection box boundary selects it

Supported edit commands

Command	What happens to the spline
Move	Translates all control vertices by the same displacement
Copy	Creates an identical spline at a new position
Rotate	Rotates all CVs around the chosen base point
Mirror	Reflects all CVs across the mirror axis
Scale	Scales all CVs uniformly from the base point
Delete	Removes the spline

Splines do not support Offset, Trim, or Extend.

Properties

General

Property	Default	Meaning
Color	256 (ByLayer)	ACI color index
Layer	0	Layer assignment
Linetype	ByLayer	Named linetype pattern
Linetype Scale	1	Scale factor on the linetype pattern
Thickness	0	Extrusion thickness

Geometry

Property	Meaning
Degree	Polynomial degree — always 3 (cubic)
Control Vertices	Coordinates of all CVs
Fit Points	Empty for CV splines; populated only for fit-point splines

Spline CV vs Spline Fit — which to use

	Spline CV	Spline Fit
Curve passes through points	First and last only (clamped)	Every clicked point exactly
Shape control	Pull CVs toward a region	Move fit points the curve must touch
Grip edit effect	CV moves → curve attracted	Fit point moves → curve re-interpolated
Best for	Smooth aesthetic curves, free-form paths	Curves that must hit specific coordinates

DXF — SPLINE entity (control-vertex form)

CV splines are saved as SPLINE entities in the DXF file, storing the degree, the knot vector, and all control vertex coordinates. All properties — color, layer, linetype, linetype scale, and thickness — round-trip without loss. The splineFlag is set to 9 (CV spline) so the form is preserved on reload. Any DXF application that supports SPLINE entities with CV data reads these correctly.