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geotheory
Asked: 2023-10-06 20:16:34 +0800 CST

ggmap/sf 仍然在错误的位置绘制点吗？

  • 772

这个老错误是否仍未解决，或者是否有合理的解决方法？

一些城市：

require(ggplot2)
require(ggmap)
require(sf)

cities = sf::read_sf('{
  "type": "FeatureCollection",
  "name": "cities",
  "crs": {
    "type": "name",
    "properties": {
      "name": "urn:ogc:def:crs:OGC:1.3:CRS84"
    }
  },
  "features": [{
      "type": "Feature",
      "properties": {
        "city": "London"
      },
      "geometry": {
        "type": "Point",
        "coordinates": [-0.13, 51.51]
      }
    },
    {
      "type": "Feature",
      "properties": {
        "city": "Rome"
      },
      "geometry": {
        "type": "Point",
        "coordinates": [12.48, 41.89]
      }
    },
    {
      "type": "Feature",
      "properties": {
        "city": "Stockholm"
      },
      "geometry": {
        "type": "Point",
        "coordinates": [18.07, 59.33]
      }
    },
    {
      "type": "Feature",
      "properties": {
        "city": "Istanbul"
      },
      "geometry": {
        "type": "Point",
        "coordinates": [28.96, 41.01]
      }
    }
  ]
}
')

还有一个 ggmap 底图：

bb = c(left = -11, bottom = 35, right = 42, top = 65)
europe = ggmap::get_stamenmap(bbox = bb, maptype = 'toner-lite', zoom = 3)

ggmap(europe) + 
  geom_sf(data = cities, inherit.aes = FALSE, col = 'red', size = 3)

在此输入图像描述

1 个回答

  1. Best Answer

    我认为问题在于ggmap使用坐标对象CoordMap来决定栅格像素的放置位置。通过切换到coord_sf（添加geom_sf图层时会发生这种情况），您将导致栅格不对齐。如果提取点的坐标，您可以简单地将它们叠加为一层geom_point：

    ggmap(europe) + 
  geom_point(data = as.data.frame(st_coordinates(cities)), aes(X, Y), 
             inherit.aes = FALSE, col = 'red', size = 3)

    在此输入图像描述

    如果您希望能够绘制更复杂的sf对象，那么我会远离ggmap并使用maptiles：

    library(maptiles)
library(tidyterra)

bb <- c(left = -11, bottom = 35, right = 42, top = 65)

europe <- matrix(bb, 2, byrow = TRUE) |>
  st_multipoint()       |> 
  st_sfc(crs = 4326)    |>
  st_transform(3857) |>
  get_tiles(provider = "Stadia.Stamen.TonerLite", zoom = 4, crop = TRUE)

ggplot() +
  geom_spatraster_rgb(data = europe) +
  geom_sf(data = cities, size = 3, color = "red") +
  coord_sf(crs = 3857, expand = FALSE, ylim = st_bbox(europe)[c(2, 4)])

    在此输入图像描述

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