I'm trying to create a simple polygon in sf and select only points within that polygon. What am I doing wrong here?
library(concaveman)
library(ggplot2)
foo.df <- data.frame("long"=c(136,137,137,136),"lat"=c(36,36,37,37))
foo.sf <- st_as_sf(foo.df, coords = c("long","lat"))
poly <- concaveman(foo.sf) ## in case points are out of order
point.df <- data.frame("long"=c(136.2,136.5,137.5),"lat"=c(36.5,36.5,36.5))
point.sf <- st_as_sf(point.df, coords = c("long","lat"))
good_points <- st_join(point.sf,poly,join=st_within)
The st_join function doesn't seem to do anything
ggplot() +
geom_sf(data = poly) +
geom_sf(data= good_points)
The problem isn't with the concaveman package
good_points <- st_join(point.sf,foo.sf,join=st_within)
ggplot() +
geom_sf(data = poly) +
geom_sf(data= good_points)
And this attempt to create a polygon throws an error
another_poly <- st_polygon(list(as.matrix(foo.df)))
good_points <- st_join(point.sf,another_poly,join=st_within)
What am I missing?
I think you are looking for st_filter. This way you'll get only the points that are found within the polygon. The good points object now contains only two points, instead of three (like in the OP).
good_points <- st_filter(point.sf, poly)
# Simple feature collection with 2 features and 0 fields
# Geometry type: POINT
# Dimension: XY
# Bounding box: xmin: 136.2 ymin: 36.5 xmax: 136.5 ymax: 36.5
# CRS: NA
# geometry
# 1 POINT (136.2 36.5)
# 2 POINT (136.5 36.5)