使用 gCentroid 在 R 中查找多个多边形的质心时保留 ID

Question

This seems like it should be simple. I have multiple polygons contained in one shapefile, and I am using the gCentroid() function from rgeos to create a bunch of centroid points. The function has an id argument which should return the parent geometry Ids if left unspecified, but this is either not working or I'm looking in the wrong spot or I misunderstood the argument.

Simple example:

library(terra)
library(rgeos)
library(sp)

v <- vect(system.file("ex/lux.shp", package="terra"))
v <- as(v, "Spatial")

#Clearly there are IDs here (albeit not unique) 
v@data[["ID_1"]] 

so when I go on to create centroids

cents <- gCentroid(v, byid = TRUE)

I don't see any associated "ID_1" slot. The issue is I will eventually be using these centroids to derive values from a raster, and will need the IDs to distinguish which polygon the values originate from.

Answer 1

The easy way would be

library(terra)
v <- vect(system.file("ex/lux.shp", package="terra"))
x <- centroids(v)

of with sf

library(sf)
y <- st_centroid(st_as_sf(v))

With rgeos you would need to do something along these lines

library(rgeos)
s <- as(v, "Spatial")
cents <- gCentroid(s, byid = TRUE)
atts <- data.frame(v)[as.integer(row.names(cents)), ]
s < SpatialPointsDataFrame(cents, atts)