LinuxCNC G5.1

G5.1 creates a quadratic B-spline in the XY plane using only the X and Y axes. I and J are incremental offsets from the start point to the control point on the X and Y axes respectively. An unspecified I or J offset is zero, so at least one of I or J must be given.

Source checked9/9 values · 2026-10-26

Specification

1 source

Language	gcode
Code	G5.1
Syntax	G5.1 X- Y- I- J-
Dialect	LinuxCNC

Parameters

Name	Data type	Description
I	real	X incremental offset from start point to control point
J	real	Y incremental offset from start point to control point

Study notes

The active plane must be G17 (XY); G5.1 is an error if another plane is active.
Only X and Y axis words are permitted; specifying any other axis is an error.
Both I and J unspecified or zero is an error.
G5.1 differs from G5: G5 creates a cubic B-spline and requires both P and Q, while G5.1 is quadratic and uses I and J offsets to one control point.
Document example: G90 G17; G0 X-2 Y4; G5.1 X2 I2 J-8 programs a parabola through the origin from X-2 Y4 to X2 Y4.