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Sheet Thickness

The sheet stage stabilizes the raw thickness traverse (sheet_thickness/data): it keeps the reliable tail of the scan, normalizes the position axis, and masks sensor error codes. It runs as part of rddac preprocess; parameters can be overridden via --config.

Property Raw Processed
Shape variable, ~(208, 2) fixed (200, 2) float32
Columns sensor_position, sheet_thickness unchanged
Position range ~50 to ~257 mm 0 to ~100 mm (normalized)
Units mm, µm unchanged
Invalid values large negative error codes (e.g. −103697) NaN

Why this stage exists

The traverse starts at the workpiece edge, so the first few readings are initialization artifacts, and wherever the sensor loses contact it reports large negative error codes instead of a thickness. Those must not leak into statistics: the mean sheet thickness of an experiment feeds the simulation matching of the pointcloud stage.

Processing steps

  1. Tail selection: only the last 200 readings are kept; the discarded head is the unstable initialization region.
  2. Position normalization: positions are shifted to start at 0, giving all experiments the same spatial reference.
  3. Error-code masking: negative readings become NaN. They are masked, not interpolated: how to treat missing thickness is a modeling decision that belongs to the consumer, not to preprocessing.
  4. Quantization: thickness to 0.01 µm, position to 0.01 mm (sensor datasheet resolutions).

Raw thickness traverses with the tail-selection cutoff (left) and the processed, position-normalized profiles (right).

Parameters

TOML key ([sheet]) Default Meaning
last_n 200 trailing readings to keep

The count of masked error codes (n_negative_masked) and the parameters used are stamped into the sheet_thickness group attributes.

Further reading