Absolute and incremental coordinates G90, G91, G92
Using G90 and G91 you have an option to choose between absolute or incremental coordinates. Incremental coordinates are very useful when you have series of similar paths to follow or when you use subprograms. You can move tool to desired point using absolute coordinates (e.g. G90 X50 Z-20), then call subprogram. Subprogram can change to incremental coordinate using G91 and after finish switch back to absolute coordinates using G90 command. When using absolute coordinates you can offset origin point using command G92 X_ Y_ Z_.
| Tool path definition using absolute coordinates: | Tool path definition using relative coordinates: |
| G90 | G90 (use absolute coordinates ) |
| G01 X0 Z2 (move to first point) | |
| G01 X0 Z2 | G91 (use relative coordinates) |
| Z0 | G01 Z-2 |
| X28 | X28 |
| X30 Z-2 | X2 Z-2 |
| Z-30 | X-28 |
| X50 Z-45 | X20 Z-15 |
| X52 | X2 |
Note that in some lines G command is missing. This means that last active G command is used.