Discrete cosine transform

Calculates discrete cosine transforms, as introduced by Dommergues and colleagues, on open outlines.

dfourier(x, nb_h, raw = FALSE, from_col, to_col, drop_coo, ...)

dfourier_i(x, nb_h, nb_pts, from_col, to_col, ...)

Arguments

x	coo_single, coo_list or mom_tbl
nb_h	int nb of harmonics. Default to 6 for dfourier, to all of them for dfourier_i
raw	logical whether to return raw and full results for dfourier
from_col, to_col	column names
drop_coo	logical whether to drop coo column (default to TRUE)
...	for generics. Useless here.
nb_pts	int nb of points for the reconstruction

Value

a list with components when applied on a single shape:

Details

Shapes must be normalized, ie using coo_bookstein before performing the dct transform.

Functions

• dfourier_i: inverse dfourier method

References

• Dommergues, C. H., Dommergues, J.-L., & Verrecchia, E. P. (2007). The Discrete Cosine Transform, a Fourier-related Method for Morphometric Analysis of Open Contours. Mathematical Geology, 39(8), 749-763. doi:10.1007/s11004-007-9124-6

• Many thanks to Remi Laffont for the original translation in R).

See also

Other morphometrics: efourier(), npoly(), opoly()

Examples

olea[1:3, ] %>% dfourier()
#> ! dfourier: 'nb_h' not provided and set to 6
#> ℹ dfourier: `raw` provided but useless here
#> # A tibble: 3 x 5
#>   var   domes view  ind   coe                   
#>   <fct> <fct> <fct> <fct> <list<coe_single[,0]>>
#> 1 Aglan cult  VD    O10   <tibble [1 × 12]>     
#> 2 Aglan cult  VL    O10   <tibble [1 × 12]>     
#> 3 Aglan cult  VD    O11   <tibble [1 × 12]>     
#> ❯mom_tbl