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Radar Positioning

The two radars have different placement requirements. They are not interchangeable and they do not share a mount.

OPS243-A

Place it 3–5 feet behind the tee, pointing down the target line.

                Ball flight direction
                ======================>

  [Tee]  ←--- 3-5 ft ---→  [OPS243-A]

Doppler measures the velocity component along the beam. Pointing down the target line means the ball's flight is nearly parallel to the beam, so the cosine error is small. Off-axis placement under-reads speed by \(\cos\theta\).

The tolerance here is forgiving — a few degrees of misalignment costs a fraction of a percent. That is why the OPS243 has no calibration step while the IWR6843 has several.

IWR6843

Do not assume it shares the OPS243 position. It has stricter mounting and measurement requirements, and its geometry values are runtime inputs rather than approximations.

You must measure and supply:

Value Flag
Antenna-centre to tee slant range --iwr6843-tee-m
Antenna-centre to net range --iwr6843-net-m
Ball-centre height above the mat --iwr6843-ball-height-m
Mount tilt from the calibration JSON, or --iwr6843-tilt-deg
Antenna-centre height from the calibration JSON, or --iwr6843-radar-height-m

Full procedure: mounting, aiming, and measuring.

Wrong geometry fails silently

A bad tee distance or tilt does not produce an error — it produces a plausible but wrong launch angle. Measure rather than estimate, and re-measure after moving or bumping the unit.

Fitting the LIS3DH inclinometer makes tilt self-correcting, which is the main reason to bother with it.

Target line reference

Club path and launch direction are reported relative to a target line, which the system cannot infer. Two flags set the reference:

  • --iwr6843-azimuth-offset-deg — azimuth of the radar boresight relative to the target line. Positive means boresight points right of the target line. With 0, club path is reported relative to boresight rather than the target.
  • --iwr6843-horizontal-phase-reference-rad — the static target-line phase from horizontal aim calibration.

See horizontal launch and club path.

Indoor considerations

Indoors, the floor produces a strong ground-bounce return that arrives just after the direct path. The launch-angle estimator models this multipath explicitly rather than trying to filter it out — which is why the net distance matters as an input, not just as a safety consideration.

Nets beyond the roughly 11-foot FSK range wrap need de-aliasing; far-flight frames are unwrapped and kept rather than dropped. Nets at or inside the wrap are unaffected.