concaveman_ggbiplot_圈圈图

参数解释：
concavity为infinite的时候就是凸多边形围栏，越小越显示细节

library(concaveman)
library(dplyr)
library(purrr)
library(sf)
library(tmap)
data(points)
polygons <- concaveman(points)
polygons
#> Simple feature collection with 1 feature and 0 fields
#> Active geometry column: polygons
#> geometry type:  POLYGON
#> dimension:      XY
#> bbox:           xmin: -122.0844 ymin: 37.3696 xmax: -122.0587 ymax: 37.3942
#> epsg (SRID):    4326
#> proj4string:    +proj=longlat +datum=WGS84 +no_defs
#>                         polygons                       geometry
#> 1 POLYGON((-122.0809 37.3736,... MULTIPOINT(-122.08441 37.38...

polygons2 <- map(unique(points$k),
                 ~ concaveman(points[points$k %in% .,])
                 ) %>% 
  map2(unique(points$k), ~ mutate(.x, k = .y)) %>% 
  reduce(rbind)
tm_shape(points) +
 tm_dots(col = "k", size = 0.1,
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