Data Schema (Export Bundle)

This page explains what is in the MD Field Mapper Pro export bundle and how to interpret it. The goal is to make it easy to do desktop QC, plotting, and post-processing without guessing what files mean.

Important: Exact SQLite table/column names can vary by build as development continues. The definitions below describe what the exported data represents (and where to find it), not rigid column naming. If you need an exact column-by-column spec, open the SQLite database and inspect the schema (instructions below).

Export bundle layout

Exports are packaged as a single folder using the iOS file exporter:

Survey_YYYYMMDD_HHMMSS_ExportPackage/
├── Database/Survey.sqlite
├── LiDAR/*.ply
├── ControlPoints/ControlPoints.csv
├── Segments/SegmentStarts.csv
└── Diagnostics/Drift.csv

If your export bundle contains additional folders/files, they are typically diagnostic or experimental outputs.

Database: SQLite (Survey.sqlite)

The SQLite database is the primary record of the survey. It stores per-sample measurements for the sweep path, relative coil height, detector audio metrics, timestamps, device attitude (yaw/pitch/roll), and segmenting.

Per-sample record contents (conceptual)

Concept	What it represents
Timestamp	Time of the sample (used to synchronize sweep, audio, and attitude channels).
Local X / Y	2D sweep path position in local LiDAR coordinates.
Local Z / height proxy	Relative coil height versus surrounding ground (proxy; not absolute elevation).
Yaw / pitch / roll	Device attitude for QC and later correction/alignment.
Audio metrics	Detector audio-derived metrics sampled alongside motion.
Segment / line id	Sweep segment identifier (L1, L2, …) created by control points.

Sampling rates: sweep sampling is selectable at 10 / 20 / 40 Hz. (LiDAR capture is adjustable separately; see below.)

How to inspect the SQLite schema

Export a bundle from the app and copy it to your desktop (Files / AirDrop).
Open Database/Survey.sqlite using a SQLite viewer (for example, DB Browser for SQLite).
Look at the Structure / Schema tab to see tables and columns.
Open the main samples table and sort by timestamp to confirm continuity.

Tip: If you send the table/column list later, this page can be upgraded to a strict column dictionary.

CSV files

ControlPoints/ControlPoints.csv

Control points are user-triggered anchors captured at fixed field features. They are used for alignment and segmentation, and each control point event can trigger a LiDAR PLY snapshot.

Segments/SegmentStarts.csv

Segment start records mark where each new sweep segment (L1, L2, …) begins. This helps you break the survey into discrete passes/lines in post-processing.

Diagnostics/Drift.csv

Diagnostic drift information recorded for QC. Use it to identify sections where tracking may have degraded (often caused by poor mounting rigidity, rapid motion, or difficult visual conditions).

LiDAR point clouds: ASCII PLY

The LiDAR/ folder contains time-segmented point clouds saved as ASCII PLY files. PLY snapshots are commonly triggered at control points so you can tie geometry to survey segments.

File type: ASCII PLY
Typical use: point cloud QC, meshing, alignment, and visualization
LiDAR capture rate: adjustable via slider from about 1–30 Hz depending on device performance

Coordinate frames and post-processing

Sweep path coordinates are in local LiDAR coordinates (not GPS).
Align to North sets a rough yaw anchor; final north alignment is done in post-processing.
Relative coil height is a proxy, best used for comparisons and QC rather than absolute elevation.

For field workflow context: see Collecting Data and Exporting Data. For the “why”: see How coil-path mapping works.