Selection of G2/G3 ABS/IJK Simulation Mode

The G2/G3 ABS/IJK Simulation Mode setting defines how the I, J, and K values are interpreted during circular interpolation simulation (G02 and G03). This is a critical setting that directly affects the accuracy of arc construction and the overall toolpath.

What this setting does

• Defines the coordinate system for the arc center:
  • IJK_INC — incremental mode (relative I, J, K values are offsets from the arc’s start point).
  • IJK_ABS — absolute mode (I, J, K values represent the coordinates of the arc center in the current coordinate system).
• If the mode does not match the actual data in the G-code, arcs may be displayed incorrectly:
  • in the opposite direction,
  • with a distorted radius,
  • with the wrong center position.
• Set in the simulator with:

  setArcIJKMode('IJK_INC'); // relative IJK
  setArcIJKMode('IJK_ABS'); // absolute IJK

How it works

1. The G-code and active IJK interpretation mode are read.
2. When calculating the arc toolpath:
   • In IJK_INC mode — the arc center is calculated as StartPoint + (I, J, K).
   • In IJK_ABS mode — the arc center is taken directly from the I, J, K coordinates.
3. The path is built based on the start point, end point, center, and rotation direction (CW/CCW).

Example

; Incremental mode (IJK_INC)
G17
G02 X50 Y50 I0 J25   ; Center offset: 0 in X, 25 in Y from start point

; Absolute mode (IJK_ABS)
G17
G02 X50 Y50 I25 J25  ; Center at (25, 25) in the coordinate system

When to use

• When loading G-code where it is known in advance that IJK values are absolute or relative.
• When changing the CAM postprocessor if it uses a different arc format.
• When debugging a program with incorrect arc display — switching the mode may fix the problem.