Rotate horizontal components to principal axes.

Applies a 2-D PCA rotation to the two horizontal signal components (DIR == "H1" and "H2") so that H1 aligns with the direction of maximum variance and H2 is orthogonal. The vertical component (DIR == "UP") is left untouched.

Usage

rotateComponents(DT)

Arguments

DT

LONG data.table(t, OCID, s, DIR) for ONE record. DIR must already be assigned.

Value

DT with s values updated in-place for DIR %in% c("H1","H2") and attr(DT, "theta") set. Returns DT unchanged when the record does not have exactly two horizontal components.

Details

This step requires a LONG table already classified with DIR values H1, H2, and UP. New processing code should usually call mapComponents() with rotate = TRUE instead of calling this helper directly.

The rotation angle theta is stored as attr(DT, "theta") in radians so that extractRecord() can persist it in the JSON sidecar.

See also

mapComponents()

Examples

t <- seq(0, 1, by = 0.1)
x <- data.table::rbindlist(list(
  data.table::data.table(t = t, OCID = "N", DIR = "H1",
                         s = sin(2 * pi * t)),
  data.table::data.table(t = t, OCID = "E", DIR = "H2",
                         s = 0.5 * cos(2 * pi * t)),
  data.table::data.table(t = t, OCID = "Z", DIR = "UP",
                         s = 0.1 * sin(2 * pi * t))
))
rotated <- rotateComponents(x)
attr(rotated, "theta")
#> [1] 3.141593