Back Distance — tdlidar_backdist

Measure the real-world distance to whatever the on-screen cross is pointing at — drive proximity zones and distance-reactive visuals up to ~20 m.

Category: Camera & Vision · Tier: Free · Needs: rear LiDAR (iPhone Pro)

What it does

Uses the rear LiDAR scanner to report the true distance, in metres, to the spot under a movable cross-hair you aim by tapping the live preview in the app. Unlike the front fader, this is metric — point it at a wall, a performer or a prop and read how far away it is, out to roughly 20 metres. Tap a new spot any time to re-aim. You also get a normalized 0–1 version for quick mapping.

OSC in

| address | type | range | rate | |—|—|—|—| | /tdlidar/backdist/meters | float | distance in metres (up to ~20 m) | LiDAR rate | | /tdlidar/backdist/norm | float | same distance, normalized 0–1 | LiDAR rate |

Outputs

out1 (CHOP) — two channels: tdlidar/backdist/meters and tdlidar/backdist/norm. The node tile previews out1.

Parameters

| par | default | what it does | |—|—|—| | OSC Port | 9000 | UDP port to listen on (match the app) |

Quick start (beginner)

  1. In the app, enable Back Distance, then tap the live preview to drop the cross on the surface you want to measure.
  2. Drop the Back Distance op — meters shows the real distance to that spot.
  3. Move the phone (or the subject) closer/further and watch meters change.
  4. Wire meters into a Text TOP to read it live, or norm straight into a 0–1 parameter for a distance-reactive effect.

Advanced patterns

  • Proximity zones (the main use): run meters through stacked Logic CHOP thresholds — < 1 m, 1–3 m, > 3 m — each enabling a different scene, like an invisible tripwire. A Lag CHOP before the Logic prevents flapping at the boundaries.
  • Distance-to-wall reactivity: map norm (or meters via a Range CHOP) into blur radius, audio reverb size, or particle spread so the visual “breathes” as the phone approaches a surface.
  • Hold on dropout: LiDAR returns can briefly fail on dark/shiny/edge surfaces; Hold CHOP (or Lag) meters so a momentary 0 doesn’t snap your mapping.
  • Combine with motion: AND a proximity zone with tdlidar_accel so an event only fires when the phone is both close and moving — e.g. a deliberate “push toward the wall”.

Gotchas

  • meters is real metric distance, norm is 0–1 — pick the one your downstream expects; don’t feed raw metres into a 0–1 parameter.
  • It measures only the spot under the cross. Re-tap in the app to aim; the channel doesn’t scan the whole frame.
  • Range tops out around 20 m, and very dark, glossy or grazing-angle surfaces can drop the return (reads near 0). Gate or hold to ride through gaps.
  • This is the rear LiDAR path — needs a Pro iPhone. For a touch-free fader on any Face-ID phone use tdlidar_frontdist instead.