Convert a clip polygon to a flat data frame for storage

Internal helper that converts a polygon (as SpatVector, sf, or anything terra::vect() accepts) into a flat data frame suitable for serializing inside a BirdFlow object's metadata. The data frame has columns id (polygon / object index), part (ring group within polygon), x, y (vertex coordinates), and hole (integer ring index: 0 for the outer ring of a part and 1..N for each distinct hole ring within the same part). The schema mirrors the matrix that terra::vect() accepts when type = "polygons", which is what dataframe_to_clip() uses to round-trip the polygon back into spatial form.

Usage

clip_to_dataframe(clip)

Arguments

clip

A polygon, in any form accepted by terra::vect().

Value

A data frame with columns id, part, x, y, hole.

Details

Storing the polygon as plain columns avoids serializing terra/sf objects (which hold C++ pointers / environments and don't survive saveRDS() or HDF5 round-trips reliably).

Earlier versions of this code stored hole as a logical, which collapsed multiple holes within one part into a single ring on round-trip; the integer index keeps each hole distinct.

See also

dataframe_to_clip() for the inverse.