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Inverse elliptic Fourier transform

Source: R/morpho_eft.R
eft_i.Rd

Reconstruct outline coordinates from elliptic Fourier coefficients.

Usage

eft_i(x, nb_h = NULL, nb_pts = 120, ..., .cols = NULL, .name = NULL)

Arguments

x

A numeric vector, list (from raw eft), list of vectors, or tibble with coe columns.

nb_h

Integer. Number of harmonics to use for reconstruction. If NULL, uses all available harmonics.

nb_pts

Integer. Number of points to reconstruct. Default is 120.

...

Additional arguments (reserved for future use).

.cols

Column name(s) to process when x is a tibble. If NULL, automatically detects columns containing coe objects.

.name

Character. Name for the output coo column when x is a tibble. If NULL, uses the pattern "colname_i" (e.g., "coe_i").

Value

  • If x is a vector or raw list: returns a matrix (nb_pts x 2) with class "xy"

  • If x is a list of vectors: returns a list of matrices

  • If x is a tibble: returns the tibble with a new coo column added

Details

Performs inverse elliptic Fourier transform to reconstruct outline coordinates from coefficients. This is useful for:

  • Visualizing shapes at different harmonic levels

  • Reconstructing shapes from PCA or other statistical analyses

  • Filtering out high-frequency noise by using fewer harmonics

If nb_h is less than the total number of harmonics in the coefficients, only the first nb_h harmonics are used (low-pass filtering).

See also

eft() for forward transform

Examples

# Single outline
coo <- matrix(runif(100), ncol = 2)
coefs <- eft(coo, nb_h = 6)

# Reconstruct with all harmonics
coo_reconstructed <- eft_i(coefs)

# Reconstruct with fewer harmonics (smoothing)
coo_smooth <- eft_i(coefs, nb_h = 3)

# From raw output
coefs_raw <- eft(coo, raw = TRUE)
eft_i(coefs_raw)
#> <xy [120 x 2]>
#>       x     y    
#>  [1,] 0.536 0.460
#>  [2,] 0.541 0.482
#>  [3,] 0.547 0.495
#>  [4,] 0.551 0.496
#>  [5,] 0.552 0.487
#>  [6,] ...   ...  
#>  [7,] 0.535 0.318
#>  [8,] 0.528 0.338
#>  [9,] 0.525 0.366
#> [10,] 0.526 0.398
#> [11,] 0.530 0.431

if (FALSE) { # \dontrun{
# Tibble workflow
library(dplyr)
bot %>%
  eft() %>%
  eft_i()

# Custom column names
bot %>%
  eft(.name = "eft") %>%
  eft_i(.cols = eft, .name = "coo_reconstructed")
} # }