docs: G38 probe to machine-coordinate conversion via #5401-#5409

[grandixximo]

Documents the official way to recover the absolute machine coordinate of a probe from the result parameters #5061-#5069.

Since #3996, #5401-#5409 report the tool length offset actually applied to motion (set by the G43 family, zeroed by G49). That makes the probe-to-machine conversion reliable whether or not a tool offset is active, so it no longer requires cancelling the offset with G49 first as the existing G38.2 example does.

Added under the G38._n_ straight probe section:

G38.2 Z-100 F100
#<zmachine> = [#5063 + #[5203 + #5220 * 20] + #5213 * #5210 + #5403]

Refs #4159

[c-morley]

Would if be possible to add a parameter that automatically calculates this anytime obe of the variables changes?

[grandixximo]

Other controllers expose the current point in two frames and subtract...

We already have the work-frame set in #5420-#5428. We are only missing the machine-frame set.

I checked and #5021-#5029 are free and can be used for machine-frame set.

Implementation is small. #5420-#5428 are already filled each line from the work-frame position; the machine set fills the same block with current + tool_offset + g5x_offset + g92_offset per axis.

What it gives:

• absolute machine position directly
• total offset per axis as [#5021 - #5420] similar to other controllers
• the machine-coordinate probe point as [#5061 + #5021 - #5420]

I'll look into it tomorrow...