Find which coordinates simplification would keep

Returns the positions of the coordinates that survive simplification, rather than the simplified geometry itself. One list per input geometry.

Usage

ga_simplify_idx(geometry, epsilon)

ga_simplify_vw_idx(geometry, epsilon)

Arguments

geometry: a GeoArrow linestring array
epsilon: the simplification tolerance; length 1 or the same length as geometry

Value

a list array of integer positions, one list per input geometry

Details

Use these when the coordinates carry data of their own, such as a timestamp or a sensor reading per vertex. Simplifying the geometry discards that alignment; the indices let you subset the other columns the same way.

ga_simplify_idx() uses Ramer-Douglas-Peucker and ga_simplify_vw_idx() uses Visvalingam-Whyatt, matching ga_simplify() and ga_simplify_vw(). Indices are 1 based and always include the first and last coordinate.

Only linestrings can be simplified this way. Any other geometry type, or a null geometry, comes back null.

References

SimplifyIdx

SimplifyVwIdx

Examples

line <- sf::st_linestring(cbind(c(0, 1, 2, 3, 4), c(0, 0.1, 0, 0.1, 0)))
g <- geoarrow::as_geoarrow_array(sf::st_sfc(line))

as.vector(ga_simplify_idx(g, 0.5))
#> <list_of<integer>[1]>
#> [[1]]
#> [1] 1 5
#>