How coil-path mapping works

MD Field Mapper Pro is built around a simple assumption: the camera center crosshair represents the coil’s effective position along the detector shaft. If that geometry is stable, LiDAR-derived local coordinates can be used to build a repeatable sweep path and tie detector audio to space.

The core idea

What you get

  • A 2D sweep path in local LiDAR coordinates (X/Y)
  • Relative coil height versus surrounding ground (a proxy, not absolute)
  • Detector audio metrics linked to time and position
  • Attitude channels: yaw / pitch / roll + timestamps
  • Segments (L1, L2, …) marked by control points

What it is not (yet)

  • No GPS/UTM export today
  • Compass-derived north is limited in accuracy
  • Final leveling and north alignment are done in post-processing
  • Bluetooth / wireless detector audio is not supported

Why rigid mounting is non-negotiable

The app treats the phone as part of the detector’s rigid body. If the phone moves independently (wobble, flex, rotation, slipping), the app will still record a path — but it will be the phone’s motion, not the coil’s.

Bottom line: handheld or loose mounts distort the sweep path and break the coil/camera geometry. Use a rigid clamp or locking action-camera style mount.

How sampling rates affect results

Practical guidance: start moderate (20 Hz sweep, mid-range LiDAR rate), then increase only after your mount and motion are stable.

Control points and segmentation

Control points are how you anchor a survey to real, repeatable features. When you tap Add CTRL PTS: the app starts a new segment (L1, L2, …) and triggers a LiDAR PLY snapshot. These anchors are used later for alignment and (eventual) georeferencing workflows.

If you want your survey to be alignable later, add control points at fixed features (corners, markers, rocks, stakes) whenever you change direction, move to a new patch, or want a reliable reference.

Why “Align to North” is only a rough anchor

The Align to North button provides a rough yaw reference by asking you to place the phone flat and rotate toward geographic north. When accepted, the outline turns green. This helps establish an initial yaw anchor, but final north alignment is intentionally performed in post-processing.

Start here

  1. Getting Started — mounting geometry, wired TRRS audio, and iPhone settings
  2. Collecting Data — field workflow (Start/Stop, overlays, control points)
  3. Exporting Data — gear icon → Export Bundle… → Files/AirDrop
  4. Working with the Data — SQLite/CSV/PLY bundle and post-processing intent

Looking to join testing? Request access on the home page: TestFlight Access.