docs: Add information on coordinate systems to Code_Overview.md
Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
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Kevin O'Connor
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@ -400,6 +400,93 @@ Useful steps:
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the micro-controller with the main klippy.py program.
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the micro-controller with the main klippy.py program.
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9. Consider adding build test cases in the test/ directory.
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9. Consider adding build test cases in the test/ directory.
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Coordinate Systems
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==================
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The position of the toolhead is primarily tracked in cartesian
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coordinates that are relative to the coordinate system specified in
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the config file. That is, the coordinate system generally does not
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change during run-time. If a request is made to alter the origin (eg,
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a `G92` command) then that effect is obtained by translating future
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commands to the existing coordinate system.
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However, in some cases it is useful to obtain the toolhead position in
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some other coordinate system and Klipper has several tools to
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facilitate that. This can be seen by running the GET_POSITION
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command. For example:
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```
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Send: GET_POSITION
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Recv: // mcu: stepper_a:-2060 stepper_b:-1169 stepper_c:-1613
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Recv: // stepper: stepper_a:457.254159 stepper_b:466.085669 stepper_c:465.382132
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Recv: // kinematic: X:8.339144 Y:-3.131558 Z:233.347121
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Recv: // toolhead: X:8.338078 Y:-3.123175 Z:233.347878 E:0.000000
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Recv: // gcode: X:8.338078 Y:-3.123175 Z:233.347878 E:0.000000
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Recv: // gcode base: X:0.000000 Y:0.000000 Z:0.000000 E:0.000000
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Recv: // gcode homing: X:0.000000 Y:0.000000 Z:0.000000
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```
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The "mcu" position (`stepper.get_mcu_position()` in the code) is the
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total number of steps the micro-controller has issued in a positive
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direction minus the number of steps issued in a negative direction
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since the micro-controller was last reset. The value reported is only
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valid after the stepper has been homed. If the robot is in motion when
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the query is issued then the reported value includes moves buffered on
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the micro-controller, but does not include moves on the look-ahead
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queue.
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The "stepper" position (`stepper.get_commanded_position()`) is the
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position for the given stepper as tracked by the kinematics code. This
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generally corresponds to the position of the carriage along its rail
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in units of millimeters and is generally relative to the
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endstop_position specified in the config file. (Some kinematics track
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the position in radians instead of millimeters.) If the robot is in
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motion when the query is issued then the reported value includes moves
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buffered on the micro-controller, but does not include moves on the
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look-ahead queue. One may use the `toolhead.flush_step_generation()`
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or `toolhead.wait_moves()` calls to fully flush the look-ahead and
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step generation code.
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The "kinematic" position (`kin.set_tag_position()` and
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`kin.calc_tag_position()`) is the cartesian position of the toolhead
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as derived from the "stepper" position and is relative to the
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coordinate system specified in the config file. This may differ from
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the requested cartesian position due to the granularity of the stepper
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motors. If the robot is in motion when `kin.set_tag_position()` is
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issued then the reported value includes moves buffered on the
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micro-controller, but does not include moves on the look-ahead
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queue. One may use the `toolhead.flush_step_generation()` or
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`toolhead.wait_moves()` calls to fully flush the look-ahead and step
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generation code.
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The "toolhead" position (`toolhead.get_position()`) is the last
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requested position of the toolhead in cartesian coordinates relative
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to the coordinate system specified in the config file. If the robot is
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in motion when the query is issued then the reported value includes
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all requested moves (even those in buffers waiting to be issued to the
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stepper motor drivers).
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The "gcode" position is the last requested position from a `G1` (or
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`G0`) command in cartesian coordinates relative to the coordinate
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system specified in the config file. This may differ from the
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"toolhead" position if a g-code transformation (eg, bed_mesh,
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bed_tilt, skew_correction) is in effect. This may differ from the
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actual coordinates specified in the last `G1` command if the g-code
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origin has been changed (eg, `G92`, `SET_GCODE_OFFSET`, `M221`). The
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`M114` command (`gcode.get_status()['gcode_position']`) will report
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the last g-code position relative to the current g-code coordinate
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system.
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The "gcode base" is the location of the g-code origin in cartesian
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coordinates relative to the coordinate system specified in the config
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file. Commands such as `G92`, `SET_GCODE_OFFSET`, and `M221` alter
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this value.
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The "gcode homing" is the location to use for the g-code origin (in
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cartesian coordinates relative to the coordinate system specified in
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the config file) after a `G28` home command. The `SET_GCODE_OFFSET`
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command can alter this value.
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Time
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Time
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====
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====
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