尝试为 R 中的多边形分配空间参考

Question

我正在尝试生成随机形状和大小的图，这些图将覆盖光栅图像的 85%。到目前为止，这是我所拥有的，但我不断收到错误消息。我已经尝试了很多不同的迭代，但消息仍然存在。如果有人能找到错误，我将不胜感激。

错误（函数（类，fdef，mtable）： 无法找到函数“proj4string<-’ for signature ‘"Polygon", "CRS"’

”的继承方法

library(sp)
library(ggplot2)
library(rgeos)
library(sf)
library(rgdal)
library(raster)

# image
site <- raster("C:/Users/ichth/OneDrive/Documents/Restoration_Implementation/Design_Project/Site_Raster.tif")

# plot size min/max in pixels
plot_size <- c(10, 25)

# find raster total area
total_area <- cellStats(site, sum)

# find area needed to cover 85%
target_area <- 0.85 * total_area

# create empty data frame 
plots <- SpatialPolygonsDataFrame(
  SpatialPolygons(list()), 
  data.frame(id = numeric(), area = numeric(), row.names = character()),
  match.ID = FALSE
)

# loop until target reached
while (sum(plots$area) < target_area) {
  
  # next plot random location and size
  x <- runif(1, xmin(site), xmax(site))
  y <- runif(1, ymin(site), ymax(site))
  size <- runif(1, plot_size[1], plot_size[2])
  
  # set coordinate system for plots
  crs(site) <- "+proj=tmerc +lat_0=24.3333333333333 +lon_0=-81 +k=0.999941177 +x_0=200000.0001016 +y_0=0 +datum=NAD83 +units=us-ft +no_defs"
  
  # create overall polygon
  pol <- Polygon(
    matrix(
      c(x, x + size, x + size, x, x, 
        y, y, y + size, y + size, y),
      ncol = 2, byrow = TRUE))
  
  # set coordinate system for plots
  proj4string(pol) <- CRS(as.character(crs(site)))
  
  # add to plots data frame
  spatial_poly <- SpatialPolygons(list(Polygons(list(pol), ID = as.character(length(plots) + 1))))
  plots <- rbind(plots, data.frame(id = length(plots) + 1, area = gArea(pol), row.names = as.character(length(plots) + 1)))
  coordinates(plots) <- c("x", "y")
  
  
  # check if target area has been reached
  if (sum(plots$area) >= target_area) {
    break
  }
  
  # plot on raster
  ggplot() +
    geom_raster(data = as.data.frame(site), aes(x = x, y = y, fill = value)) +
    geom_polygon(data = as.data.frame(plots), aes(x = x, y = y, fill = area), color = "white", alpha = 0.7) +
    coord_equal() +
    theme_void() +
    scale_fill_gradient(low = "white", high = "red")
}

Error in (function (classes, fdef, mtable)  : 
  unable to find an inherited method for function ‘proj4string<-’ for signature ‘"Polygon", "CRS"’

Answer 1

Polygon

对象是纯几何的，没有坐标参考。因此，我认为导致您的错误消息的最小说明是：

> pol = Polygon(coords=cbind(c(0,1,1,0,0), c(0,0,1,1,0)))
> proj4string(pol)=CRS("+init=epsg:4326")
Error in (function (classes, fdef, mtable)  : 
  unable to find an inherited method for function ‘proj4string<-’ for signature ‘"Polygon", "CRS"’
> 

SpatialPolygons

确实有坐标系，您已经编写了代码来构造它，所以我假设您知道如何为您的数据执行此操作。这是我如何用我的例子来做的：

> spol = SpatialPolygons(list(Polygons(list(pol),ID=1)))
> proj4string(spol)=CRS("+init=epsg:4326")

你可以在一行中用一个额外的参数来做到这一点

SpatialPolygons

：

> spol = SpatialPolygons(
       list(Polygons(list(pol),ID=1)),
       proj4string=CRS("+init=epsg:4326")
       )
>