将 `st_bbox()` 的结果转换为其他 CRS
Transform result of `st_bbox()` to other CRS
是否有一种简单的方法可以将简单特征(sf
对象)的边界转换为另一个 CRS?
函数st_bbox()
的结果是classbbox
。无法使用 st_transform()
将其转换为另一个 CRS。
我正在使用基于 EPSG: 28992
的计算边界框:
sf::st_bbox(xmin = 187470, xmax =194587,
ymin = 409753, ymax = 412715,
crs = st_crs(28992))
现在我想把这个盒子变成EPSG:4326
一种方法是制作一个中间体 sfc_MULTIPOINT
,将其转换为 4326,然后从该对象中提取边界框:
pts <- st_multipoint(rbind(c(187470, 409753), c(194587, 412715))) %>% st_sfc(crs = st_crs(28992))
pts <- pts %>% st_transform(crs = 4326)
st_bbox(pts)
xmin ymin xmax ymax
5.856639 51.675634 5.959866 51.701799
bbox
对象有一个st_as_sfc
方法,所以我们可以这样转换bbox
:
library(sf)
bb = sf::st_bbox(c(xmin = 187470, xmax =194587,
ymin = 409753, ymax = 412715),
crs = st_crs(28992))
bb_ll = st_bbox(
st_transform(
st_as_sfc(bb),
4326
)
)
# or pipey
library(magrittr)
bb_ll = bb %>%
st_as_sfc() %>%
st_transform(crs = 4326) %>%
st_bbox()
bb_ll
xmin ymin xmax ymax
5.856639 51.675176 5.959866 51.702257
如@spacedman 所述,一个坐标系中的矩形可能不是另一个坐标系中的矩形。有些坐标系比其他坐标系弯曲得多!
为了更安全地变换边界框,您可以使用 st_make_grid(n = whatever) 添加顶点。
# pipey code to show the steps clearly
library(sf)
library(dplyr)
bb_better_reproj = bb_orig %>%
st_make_grid(n=10) %>% #this also makes it into a polygon
st_transform(crs = 4326) %>%
st_bbox()
这不是 100% 安全,但比仅变换矩形多边形(仅变换角顶点,中间不变换)要好。网格顶点太多真的很慢。我发现 ~10-20 在大多数情况下效果很好。
示例(使用与 OP 不同的坐标参考系统 (CRS) 进行说明):
library(sf)
library(dplyr)
bb_orig = st_bbox(c(xmin = 40, xmax =-40,
ymin = 45, ymax = 55),
crs = st_crs(4326)) #lag/long
new_crs = 3995 # arctic polar stereographic
bb_simple_reproj = bb_orig %>%
st_as_sfc() %>%
st_transform(crs=new_crs) %>%
st_bbox
bb_better_reproj = bb_orig %>%
st_make_grid(n=10) %>%
st_transform(crs = new_crs) %>%
st_bbox()
# 100 random points inside the original bounding box (grey)
sample_from_bb_orig = st_sample(st_as_sfc(bb_orig), 1000) %>%
st_transform(new_crs)
plot(st_geometry(sample_from_bb_orig), col="grey")
# if the bbox was only transformed as simple rectangle we would get (red):
# red points indicate those missed by the simple bbox reprojection -- note that many are missed!
plot(st_geometry(st_as_sfc(bb_simple_reproj)), border="red", add=TRUE)
plot(st_difference(sample_from_bb_orig, st_as_sfc(bb_simple_reproj)) , col="red", add=TRUE)
# using 'better' repojection, with more vertices added (blue)
# blue points indicate those missed by the simple bbox reprojection
plot(st_geometry(st_as_sfc(bb_better_reproj)), border="blue", add=TRUE)
plot(st_difference(sample_from_bb_orig, st_as_sfc(bb_better_reproj)) , col="blue", pch="x", add=TRUE)
是否有一种简单的方法可以将简单特征(sf
对象)的边界转换为另一个 CRS?
函数st_bbox()
的结果是classbbox
。无法使用 st_transform()
将其转换为另一个 CRS。
我正在使用基于 EPSG: 28992
的计算边界框:
sf::st_bbox(xmin = 187470, xmax =194587,
ymin = 409753, ymax = 412715,
crs = st_crs(28992))
现在我想把这个盒子变成EPSG:4326
一种方法是制作一个中间体 sfc_MULTIPOINT
,将其转换为 4326,然后从该对象中提取边界框:
pts <- st_multipoint(rbind(c(187470, 409753), c(194587, 412715))) %>% st_sfc(crs = st_crs(28992))
pts <- pts %>% st_transform(crs = 4326)
st_bbox(pts)
xmin ymin xmax ymax
5.856639 51.675634 5.959866 51.701799
bbox
对象有一个st_as_sfc
方法,所以我们可以这样转换bbox
:
library(sf)
bb = sf::st_bbox(c(xmin = 187470, xmax =194587,
ymin = 409753, ymax = 412715),
crs = st_crs(28992))
bb_ll = st_bbox(
st_transform(
st_as_sfc(bb),
4326
)
)
# or pipey
library(magrittr)
bb_ll = bb %>%
st_as_sfc() %>%
st_transform(crs = 4326) %>%
st_bbox()
bb_ll
xmin ymin xmax ymax
5.856639 51.675176 5.959866 51.702257
如@spacedman 所述,一个坐标系中的矩形可能不是另一个坐标系中的矩形。有些坐标系比其他坐标系弯曲得多!
为了更安全地变换边界框,您可以使用 st_make_grid(n = whatever) 添加顶点。
# pipey code to show the steps clearly
library(sf)
library(dplyr)
bb_better_reproj = bb_orig %>%
st_make_grid(n=10) %>% #this also makes it into a polygon
st_transform(crs = 4326) %>%
st_bbox()
这不是 100% 安全,但比仅变换矩形多边形(仅变换角顶点,中间不变换)要好。网格顶点太多真的很慢。我发现 ~10-20 在大多数情况下效果很好。
示例(使用与 OP 不同的坐标参考系统 (CRS) 进行说明):
library(sf)
library(dplyr)
bb_orig = st_bbox(c(xmin = 40, xmax =-40,
ymin = 45, ymax = 55),
crs = st_crs(4326)) #lag/long
new_crs = 3995 # arctic polar stereographic
bb_simple_reproj = bb_orig %>%
st_as_sfc() %>%
st_transform(crs=new_crs) %>%
st_bbox
bb_better_reproj = bb_orig %>%
st_make_grid(n=10) %>%
st_transform(crs = new_crs) %>%
st_bbox()
# 100 random points inside the original bounding box (grey)
sample_from_bb_orig = st_sample(st_as_sfc(bb_orig), 1000) %>%
st_transform(new_crs)
plot(st_geometry(sample_from_bb_orig), col="grey")
# if the bbox was only transformed as simple rectangle we would get (red):
# red points indicate those missed by the simple bbox reprojection -- note that many are missed!
plot(st_geometry(st_as_sfc(bb_simple_reproj)), border="red", add=TRUE)
plot(st_difference(sample_from_bb_orig, st_as_sfc(bb_simple_reproj)) , col="red", add=TRUE)
# using 'better' repojection, with more vertices added (blue)
# blue points indicate those missed by the simple bbox reprojection
plot(st_geometry(st_as_sfc(bb_better_reproj)), border="blue", add=TRUE)
plot(st_difference(sample_from_bb_orig, st_as_sfc(bb_better_reproj)) , col="blue", pch="x", add=TRUE)