Identify if point over land or ocean using lat/lon in R with confidence metric

Question

How can I determine whether a coordinate is above land or ocean with a confidence metric in R?

I've used the sf package method described in another question: Given Lat and Lon identify if point over land or ocean using R

#Obtain latitude and logitude values.

lat <- filtered.records.coord$lat
lon <- filtered.records.coord$lon

#Place the values into a data frame.

points <- data.frame("Var1" = lon, "Var2" = lat)

#Find which points fall over land

pts <- st_as_sf(points, coords=1:2, crs=4326)
ii <- !is.na(as.numeric(st_intersects(pts, world)))

#Combine GPS results with record information.

filtered.records.coord$land <- ii

However, is there a way to determine if a coordinate is by the coastline for example and not far inland? Or some sort of confidence to the TRUE or FALSE offered by the sf package? I wish to identify borderline points.

Answer 1

You can make a buffer around the coastline - for a reproducible example consider this answer https://sg-links.stackoverflow.email/ls/click?upn=FhKQFemTFIJzn5ywFPMHvtCTWJMlhUAoxeQEKPe-2F76iSWxQbyBanTDlroRJoYkIAkWTqwFBDNPaoOfLZd-2FHH7IQzhdqI1ZTkZwpnKrlcpQZAAviPci2Ox14Qyi2B0ALeoOYdHQHfso4herTCdsxWWEIQH5qFQQy-2Bed-2FGSgd2vHV-2FLXpObWnzjDla9xNj9E8buIzy_TXecCV1o-2FnwmKOmfF3Vc4AnbxbOAOcXmfIBDIp2OEBF-2BEkS0eTcSs9AX88HTdAqn6lazX9epCFRCv9TzY3CbLvGqVrwuJEzOpZvTAJuCr-2FeMdb7WTeBeVr-2BMD9CHLfM7elGZot1RtvEdBN2Bkrdz4j7YtTaUnZvvixbWiKyt3w2PCsTOdUCqdLmQ8ue1JQv-2Byq83rU2aNL5J1oBo67A0g4aX0Nv2hbyktZ2OFmJ2Hr8-3D - and interpret the points in buffer zone as "uncertain" / as opposed to certainly land and certainly sea.