在多邊形中生成規則間隔的點

Question

有沒有辦法使用R在多邊形內生成規則間隔（例如，相隔500米）的點？ 我一直在嘗試使用sp包，但似乎無法定義一組彼此間隔一定距離的點。 我的目標是生成點，然后將它們的緯度/經度坐標提取到新的數據幀中。 任何幫助將非常感激！ 謝謝

Answer 1

相當直接， 幾乎開箱即用。

由於OP沒有分享數據，因此請將您的座位置於垂直位置並讓我們飛往巴黎 。 在那里，我們將調整地geosphere功能，在它的幫助下，我們將巴黎的形狀分成相距500米（垂直和水平）的lon / lat坐標。

# Load necessary libraries.
library(raster)
library(geosphere)
library(tidyverse)
library(sp)

# This is an adapted version of geosphere's destPoint() function that works with
# changing d (distance).
destPoint_v <- function (x, y, b, d, a = 6378137, f = 1/298.257223563, ...) 
{
    r <- list(...)$r
    if (!is.null(r)) {
        return(.old_destPoint(x, y, b, d, r = r))
    }
    b <- as.vector(b)
    d <- as.vector(d)
    x <- as.vector(x)
    y <- as.vector(y)
    p <- cbind(x, y, b, d)
    r <- .Call("_geodesic", as.double(p[, 1]), as.double(p[, 2]), 
               as.double(p[, 3]), as.double(p[, 4]), 
               as.double(a), as.double(f), 
               PACKAGE = "geosphere")
    r <- matrix(r, ncol = 3, byrow = TRUE)
    colnames(r) <- c("lon", "lat", "finalbearing")
    return(r[, 1:2, drop = FALSE])
}

# Data can be downloaded from 
# http://osm13.openstreetmap.fr/~cquest/openfla/export/communes-20190101-shp.zip
# or 
# https://www.data.gouv.fr/en/datasets/decoupage-administratif-communal-francais-issu-d-openstreetmap/
# ("Export simple de janvier 2019 (225Mo)")

# Load shapefile.
# shp <- raster::shapefile("Dropbox/work/crema/communes-20190101-shp/communes-20190101.shp")
# Extract Paris.
paris <- shp[shp$nom == "Paris", ]

# Set distance of points in meters.
dist <- 500

# Extract bounding box from Paris' SpatialPolygonDataFrame. 
bbox <- raster::extent(paris)

# Calculate number of points on the vertical axis.
ny <- ceiling(geosphere::distGeo(p1 = c(bbox@xmin, bbox@ymin), 
                               p2 = c(bbox@xmin, bbox@ymax)) / dist)
# Calculate maximum number of points on the horizontal axis. 
# This needs to be calculated for the lowermost and uppermost horizontal lines
# as the distance between latitudinal lines varies when the longitude changes. 
nx <- ceiling(max(geosphere::distGeo(p1 = c(bbox@xmin, bbox@ymin), 
                                   p2 = c(bbox@xmax, bbox@ymin)) / dist,
                geosphere::distGeo(p1 = c(bbox@xmin, bbox@ymax), 
                                   p2 = c(bbox@xmax, bbox@ymax)) / dist))

# Create result data frame with number of points on vertical axis.
df <- data.frame(ny = 1:ny)

# Calculate coordinates along the vertical axis.
pts <- geosphere::destPoint(p = c(bbox@xmin, bbox@ymin), 
                            b = 0, d = dist * (1:ny - 1))
df$x <- pts[, 1]
df$y <- pts[, 2]

# Add points on horizontal axis.
df <- tidyr::crossing(nx = 1:nx, df)

# Calculate coordinates.
pts <- destPoint_v(df$x, df$y, b = 90, 500 * (df$nx - 1))

# Turn coordinates into SpatialPoints.
pts <- SpatialPoints(cbind(pts[, 1], pts[, 2]), proj4string = CRS(proj4string(paris)))

# Cut to boundaries of Paris.
result <- raster::intersect(pts, paris)

# Plot result.
plot(result)
title("Paris in Points")

有點像魚，不是嗎？

Answer 2

這是一種方法，假設你有一個lonlat多邊形，首先將它轉換為平面crs（不像使用destPoint的Roman解決方案那樣漂亮）。

包和示例數據

library(raster)
library(rgdal)
p <- shapefile(system.file("external/lux.shp", package="raster"))[1,]

轉換為平面crs（選擇一個與您的數據匹配！）

putm <- spTransform(p, "+proj=utm +zone=32 +datum=WGS84")

創建一個分辨率為500米的柵格，柵格化多邊形並轉換為點

r <- raster(putm, res=500)
r <- rasterize(putm, r)
pts <- rasterToPoints(r, spatial=TRUE)

將點轉換為lon / lat並繪制結果

pts_lonlat <- spTransform(pts, "+proj=longlat +datum=WGS84")
result <- coordinates(pts_lonlat)

plot(p)
points(result, pch="+", cex=.5)

（看起來像一頭大象）