Calibrating fixture positions

Aiming a fixture at a point in the room only works if LMX knows where the fixture actually is. Calibration works that out from the fixture itself: point it at four known targets, and LMX solves backwards for the position and orientation that make those four aims true.

It is the mathematical inverse of the live aiming solver, so a calibrated fixture aims accurately by construction.

Open it with CALIBRATE.

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Before you start

You need four calibration targets - real, identifiable points in the room whose coordinates you know: a mark on the stage, a corner, a seat, a flight case. Create them and mark them as calibration slots 1 to 4:

CREATE TARGET 1 NAME "DSL mark"  POS 2.0 1.5 0 CALIBRATE 1
CREATE TARGET 2 NAME "DSR mark"  POS 8.0 1.5 0 CALIBRATE 2
CREATE TARGET 3 NAME "USL mark"  POS 2.0 6.0 0 CALIBRATE 3
CREATE TARGET 4 NAME "USR mark"  POS 8.0 6.0 0 CALIBRATE 4
LIST TARGETS

Spread them out. Four points clustered together, or all in a straight line, do not constrain the solve and the answer will be poor.

An existing target can be promoted or demoted:

UPDATE TARGET 3 CALIBRATE 2
UPDATE TARGET 3 CALIBRATE REMOVE

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Running a calibration

1. CALIBRATE opens the window. The left pane lists every fixture with pan and tilt; pick one and press Calibrate.
2. LMX takes exclusive control of that fixture while the session runs, so cues and faders cannot move it under you. (The emergency state still wins.)
3. For each of the four targets in turn: drive the pan and tilt dials until the beam is centred on the real target, then press Next. The dials behave exactly like the programmer’s.
4. After the fourth capture the button reads Finish. Pressing it solves the pose and writes the position and orientation back to the fixture.

Cancel, or closing the window, releases the fixture and discards the captures. Position and orientation values typed directly into the boxes are saved as you make them, independently of the session.

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Getting a good result

• Use a tight beam: zoom in and focus up before you start. Centring a wide wash by eye is guesswork.
• Aim at the same physical feature every time - the centre of the mark, not “about there”.
• Four well-spread targets beat four accurate ones that are close together.
• If the solved position is obviously wrong, the usual cause is a target whose stored coordinates are not where the mark really is. Re-measure the target before re-calibrating the fixture.

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Doing it by hand instead

If you have a drawing, you can just type the numbers:

UPDATE FIXTURE 12 POS 5.0 0.0 6.2
UPDATE FIXTURE 12 ORI 0 -40 0

Calibration exists for the case where the drawing is optimistic and the truss is where the truss is.

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See also

Targets and aiming · Fixtures and patching · 2D stage layout