为什么st_join(ob1，ob2，left = True)返回具有比ob1更多功能的sf对象

st_join()的默认判定为st_intersects，对于touch 几何形状，也是TRUE.

intersects - A and B are not disjoint
disjoint - A and B have no points in common
( https://r-spatial.org/book/03-Geometries.html#sec-de9im )

就你的情况而言，你似乎是st_within之后.

within B的点都不在A之外

首先让我们可视化这些功能的关联:

library("sf")
#> Linking to GEOS 3.11.2, GDAL 3.6.2, PROJ 9.2.0; sf_use_s2() is TRUE
library("tidyverse")

map1 <- st_as_sfc(c("POLYGON((0 0 , 0 1 , -1 1 , -1 0, 0 0))",
                    "POLYGON((0 0 , 0 2 , 2 2 , 2 0, 0 0 ))", 
                    "POLYGON((0 0 , 0 -0.5 , -0.5 -0.5 , -0.5 0, 0 0))")) %>% 
  st_sf(ID = paste0("poly", 1:3),
        att1 = c(letters[1:3]))

map2 <- st_as_sfc(c("POLYGON((0 0 , 0 0.5 , -0.5 .5 , -0.5 0, 0 0))",
                    "POLYGON((-0.5 0 , -0.5 1 , -1 1 , -1 0 , -0.5 0))",
                    "POLYGON((0 0 , 0 1 , 1 1 , 1 0 , 0 0))",
                    "POLYGON((1 1 , 1 2 , 2 2 , 2 1 , 1 1))",
                    "POLYGON((0 0 , 0 -0.25 , -0.25 -0.25 , -0.25 0 , 0 0))")) %>% 
  st_sf(ID = paste0("poly", 4:8)) %>%
  mutate(att2 = c(LETTERS[1:5]))

ggplot() +
  geom_sf(data = map1, aes(fill = "map1"), linewidth = 5,) +
  geom_sf(data = map2, aes(fill = "map2"), color = "white", , linewidth = 1, alpha = .2) +
  geom_sf_label(data = map1, aes(label = ID, fill = "map1")) +
  geom_sf_label(data = map2, aes(label = ID, fill = "map2"), color = "white") +
  theme_minimal()

st_join(... , join = st_intersects)(默认):

st_join(map2, map1, left = TRUE, join = st_intersects)
#> Simple feature collection with 12 features and 4 fields
#> Geometry type: POLYGON
#> Dimension:     XY
#> Bounding box:  xmin: -1 ymin: -0.25 xmax: 2 ymax: 2
#> CRS:           NA
#> First 10 features:
#>      ID.x att2  ID.y att1                              .
#> 1   poly4    A poly1    a POLYGON ((0 0, 0 0.5, -0.5 ...
#> 1.1 poly4    A poly2    b POLYGON ((0 0, 0 0.5, -0.5 ...
#> 1.2 poly4    A poly3    c POLYGON ((0 0, 0 0.5, -0.5 ...
#> 2   poly5    B poly1    a POLYGON ((-0.5 0, -0.5 1, -...
#> 2.1 poly5    B poly3    c POLYGON ((-0.5 0, -0.5 1, -...
#> 3   poly6    C poly1    a POLYGON ((0 0, 0 1, 1 1, 1 ...
#> 3.1 poly6    C poly2    b POLYGON ((0 0, 0 1, 1 1, 1 ...
#> 3.2 poly6    C poly3    c POLYGON ((0 0, 0 1, 1 1, 1 ...
#> 4   poly7    D poly2    b POLYGON ((1 1, 1 2, 2 2, 2 ...
#> 5   poly8    E poly1    a POLYGON ((0 0, 0 -0.25, -0....

st_join(... , join = st_within):

st_join(map2, map1, left = TRUE, join = st_within)
#> Simple feature collection with 5 features and 4 fields
#> Geometry type: POLYGON
#> Dimension:     XY
#> Bounding box:  xmin: -1 ymin: -0.25 xmax: 2 ymax: 2
#> CRS:           NA
#>    ID.x att2  ID.y att1                              .
#> 1 poly4    A poly1    a POLYGON ((0 0, 0 0.5, -0.5 ...
#> 2 poly5    B poly1    a POLYGON ((-0.5 0, -0.5 1, -...
#> 3 poly6    C poly2    b POLYGON ((0 0, 0 1, 1 1, 1 ...
#> 4 poly7    D poly2    b POLYGON ((1 1, 1 2, 2 2, 2 ...
#> 5 poly8    E poly3    c POLYGON ((0 0, 0 -0.25, -0....

^{创建于2024年4月15日，共有reprex v2.1.0个}