r - 来自多边形输入的点网格

Question

我正在编写一个脚本，该脚本采用在 google earth 中创建的输入 KML 文件，并在多边形内绘制坐标点网格。

到目前为止，我有多边形输入和多边形边界框的点网格，但我只想在多边形内部有点。

我尝试使用over() 函数执行此操作，但它不起作用。有什么建议吗？

你可以下载我的测试KML文件HERE。

library(rgdal)
library(sp)
library(maptools)

# ogrInfo() to find layer name... not as labelled in Google Earth?!
my.poly = readOGR(ds = "PolyNYC.kml", layer = "PolyNYC") 
proj4string(my.poly) <- "+proj=longlat +datum=WGS84 +no_defs"

# Creating grid of points
grdpts <- makegrid(my.poly)

# Converting from df to spdf
coords = cbind(grdpts$x1, grdpts$x2)
sp = SpatialPoints(coords)
spdf = SpatialPointsDataFrame(coords, grdpts, proj4string = CRS(proj4string(my.poly)))

# Using over() to select only those points in the polygon
inPoly = over(spdf, my.poly)
# This is not working

# Plotting the polygon with the points overlaid.
plot(my.poly)
points(spdf, pch = 3, col = "red")

#kmlPoints(obj = spdf, kmlfile = "BBoxFromPoly.kml", kmlname = "Testing123")

Answer 1

我将展示一个使用library(sf) 的解决方案，它是library(sp) 的继承者

加载数据

library(sf)

## read the kml
my.poly <- sf::st_read("~/Downloads/PolyNYC.kml")

## create a grid of points
grdpts <- sf::st_make_grid(my.poly, what = "centers")

## convert it to an `sf` object, as opposed to an `sfc`
my.points <- sf::st_sf(grdpts)

查看数据

要查看地图上的对象，我正在使用我的 googleway 包将其绘制在 Google 地图上（因此您需要 API 密钥），但您可以使用 leaflet 或任何您想要的地图

library(googleway)

set_key("your_api_key_here")

google_map() %>%
  add_polygons(my.poly) %>%
  add_markers(my.points)

多边形中的点

您可以使用函数sf::st_join() 加入几何图形

pointsInside <- sf::st_join(x = my.points, y = my.poly, left = FALSE)

# Simple feature collection with 59 features and 2 fields
# geometry type:  POINT
# dimension:      XY
# bbox:           xmin: -74.1754 ymin: 40.63513 xmax: -73.75675 ymax: 40.8514
# epsg (SRID):    4326
# proj4string:    +proj=longlat +datum=WGS84 +no_defs
# First 10 features:
#   Name Description                   geometry
# 1  TestLayerNYC             POINT (-74.08237 40.63513)
# 2  TestLayerNYC             POINT (-74.03585 40.63513)
# 3  TestLayerNYC              POINT (-74.1754 40.65916)
# 4  TestLayerNYC             POINT (-74.12889 40.65916)
# 5  TestLayerNYC             POINT (-74.08237 40.65916)
# 6  TestLayerNYC             POINT (-74.03585 40.65916)
# 7  TestLayerNYC             POINT (-73.80326 40.65916)
# 8  TestLayerNYC              POINT (-74.1754 40.68319)
# 9  TestLayerNYC             POINT (-74.12889 40.68319)
# 10 TestLayerNYC             POINT (-74.08237 40.68319)

这里，pointsInside 是多边形内的所有点

查看结果

google_map() %>%
  add_polygons(my.poly) %>%
  add_markers(pointsInside)