Question

我试图获取一组点的坐标，这些点在多边形内定义网格（我有一个shapefile）。看起来最简单的事情就是创建一个点网格，然后将这些点过滤到只有多边形内的点。我查看了https://gis.stackexchange.com/questions/133625/checking-if-points-fall-within-polygon-shapefile和Convert a shapefile from polygons to points?，并根据答案在那里尝试了这个：

library(rgdal) city_bdry <- readOGR("Boundaries - City", "geo_export_32ded882-2eab-4eaa-b9da-a18889600a40") res <- 0.01 bb <- bbox(city_bdry) gt <- GridTopology(cellcentre.offset = bb[,1], cellsize = c(res, res), cells.dim = c(diff(bb[,1]), diff(bb[2,])) / res + 1) pts <- SpatialPoints(gt, proj4string = CRS(proj4string(city_bdry))) ov <- over(pts, city_bdry)

然而，结果并不包括与多边形重叠的点的实际坐标，因此对我来说没用。如何将这些信息包含在数据框中？或者，有没有更简单的方法来做我想做的事情？

我可以从https://data.cityofchicago.org/Facilities-Geographic-Boundaries/Boundaries-City/ewy2-6yfk
下载我使用的shapefile

Answer 1

如果我找对你，你可以试试

library(rgdal)
download.file("https://data.cityofchicago.org/api/geospatial/ewy2-6yfk?method=export&format=Shapefile", tf<-tempfile(fileext = ".zip"), mode="wb")
unzip(tf, exdir=dir<-file.path(tempdir(), "Boundaries - City"))
city_bdry <- readOGR(dir, tools::file_path_sans_ext((list.files(dir)[1])))
res <- 0.01
bb <- bbox(city_bdry)
gt <- GridTopology(cellcentre.offset = bb[,1], cellsize = c(res, res), 
                   cells.dim = c(diff(bb[,1]), diff(bb[2,])) / res + 1)
pts <- SpatialPoints(gt, proj4string = CRS(proj4string(city_bdry)))

ov <- sp::over(pts, as(city_bdry, "SpatialPolygons"))
pts_over <- pts[!is.na(ov)]

plot(city_bdry)
points(pts_over)
coordinates(pts_over)

Answer 2

使用splancs::inout()。

<强> 1。获取多边形的轮廓

outline <- mySpatialPolygonsDataFrame@polygons[[2]]@Polygons[[1]]@coords

<强> 2。使用inout（）查找大纲中的哪些点

library(splancs)
pts_in_polygon <- points[inout(points,outline), ]

Note: very similar to the answer I provide to create an irregularly shaped grid (especially for kriging.)

Answer 3

您也可以通过简单地使用[ yourPoints[yourPolygons, ]对数据进行子集来实现这一目标：

library(raster)
bra <- getData(country = "BRA", level = 1)

pts <- makegrid(bra, 100)
pts <- SpatialPoints(pts, proj4string = CRS(proj4string(bra)))

coordinates(pts[bra, ])

在多边形内查找网格点的坐标

3 个答案: