如何使用 geom_sf 绘制 PostGIS 几何图形？答案

【问题标题】：How do I plot PostGIS geometries using geom_sf?如何使用 geom_sf 绘制 PostGIS 几何图形？
【发布时间】：2018-08-30 23:20:28
【问题描述】：

数据源是具有 PostGIS 几何类型的 PostgreSQL 数据库。使用RPostgreSQL 包将我想要的数据直接从SQL 查询到data.frame 没有问题。

由于 R 抱怨原始几何类型，我在 SQL 查询中的几何上使用ST_AsText()，以便它们在data.frame 中存储为character 类型。我有三种类型：POINT、LINESTRING 和 POLYGON。请注意，我的数据是几何（例如笛卡尔 x、y、z 坐标），而不是地图投影的地理。

在制作 MWE 时遇到了一些麻烦，因为我必须用换行符分隔每个 LINESTRING 和 POLYGON 元素，否则 r 认为我缺少括号。可能是一个错误？不管怎样，这里是 MWE：

tmpdf <- data.frame(id = seq(1,6,1),
                point = c("POINT(-186.552366 -69.56887)","POINT(151.826334 -19.119682)","POINT(-189.013302 -67.107934)","POINT(-195.575798 59.220114)","POINT(103.01777 62.501362)","POINT(135.009938 55.118554)"),
                linestr = c("LINESTRING(186.547856450189 -46.4485209972227,182.523886136587 -87.3045772259105,170.606614118262 -126.59055812607,151.254014475596 -162.79672548354,125.209796759794 -194.531696591426,93.4748256519081 -220.575914307228,65.3272038227373 -235.621131625452,36.2687622716732 -244.435913500765,-9.05803921416017 -248.900213788796,-54.3848406999935 -244.435913500765,-97.9697586242894 -231.214573193132,-138.137849033921 -209.744281559306,-173.34547474097 -180.850129866096,-202.239626434179 -145.642504159047,-221.510885247941 -109.588514788964,-228.270643805406 -87.3045772259111,-232.294614119009 -46.4485209972234,-228.270643805406 -5.59246476853568,-216.353371787081 33.6935161316239,-197.000772144416 69.8996834890942,-170.956554428614 101.63465459698,-139.221583320728 127.678872312782,-103.015415963258 147.031471955448,-63.7294350630982 158.948743973773,-22.8733788344104 162.972714287376,17.9826773942774 158.948743973774,57.2686582944371 147.031471955449,93.4748256519074 127.678872312783,125.209796759793 101.634654596981,151.254014475596 69.8996834890953,170.606614118262 33.6935161316251,182.523886136587 -5.59246476853451,186.547856450189 -46.4485209972227)",
                            "LINESTRING(186.547856450189 -46.4485209972227,182.523886136587 -87.3045772259105,170.606614118262 -126.59055812607,151.254014475596 -162.79672548354,125.209796759794 -194.531696591426,93.4748256519081 -220.575914307228,65.3272038227373 -235.621131625452,36.2687622716732 -244.435913500765,-9.05803921416017 -248.900213788796,-54.3848406999935 -244.435913500765,-97.9697586242894 -231.214573193132,-138.137849033921 -209.744281559306,-173.34547474097 -180.850129866096,-202.239626434179 -145.642504159047,-221.510885247941 -109.588514788964,-228.270643805406 -87.3045772259111,-232.294614119009 -46.4485209972234,-228.270643805406 -5.59246476853568,-216.353371787081 33.6935161316239,-197.000772144416 69.8996834890942,-170.956554428614 101.63465459698,-139.221583320728 127.678872312782,-103.015415963258 147.031471955448,-63.7294350630982 158.948743973773,-22.8733788344104 162.972714287376,17.9826773942774 158.948743973774,57.2686582944371 147.031471955449,93.4748256519074 127.678872312783,125.209796759793 101.634654596981,151.254014475596 69.8996834890953,170.606614118262 33.6935161316251,182.523886136587 -5.59246476853451,186.547856450189 -46.4485209972227)",
                            "LINESTRING(186.547856450189 -46.4485209972227,182.523886136587 -87.3045772259105,170.606614118262 -126.59055812607,151.254014475596 -162.79672548354,125.209796759794 -194.531696591426,93.4748256519081 -220.575914307228,65.3272038227373 -235.621131625452,36.2687622716732 -244.435913500765,-9.05803921416017 -248.900213788796,-54.3848406999935 -244.435913500765,-97.9697586242894 -231.214573193132,-138.137849033921 -209.744281559306,-173.34547474097 -180.850129866096,-202.239626434179 -145.642504159047,-221.510885247941 -109.588514788964,-228.270643805406 -87.3045772259111,-232.294614119009 -46.4485209972234,-228.270643805406 -5.59246476853568,-216.353371787081 33.6935161316239,-197.000772144416 69.8996834890942,-170.956554428614 101.63465459698,-139.221583320728 127.678872312782,-103.015415963258 147.031471955448,-63.7294350630982 158.948743973773,-22.8733788344104 162.972714287376,17.9826773942774 158.948743973774,57.2686582944371 147.031471955449,93.4748256519074 127.678872312783,125.209796759793 101.634654596981,151.254014475596 69.8996834890953,170.606614118262 33.6935161316251,182.523886136587 -5.59246476853451,186.547856450189 -46.4485209972227)",
                            "LINESTRING(186.547856450189 -46.4485209972227,182.523886136587 -87.3045772259105,170.606614118262 -126.59055812607,151.254014475596 -162.79672548354,125.209796759794 -194.531696591426,93.4748256519081 -220.575914307228,65.3272038227373 -235.621131625452,36.2687622716732 -244.435913500765,-9.05803921416017 -248.900213788796,-54.3848406999935 -244.435913500765,-97.9697586242894 -231.214573193132,-138.137849033921 -209.744281559306,-173.34547474097 -180.850129866096,-202.239626434179 -145.642504159047,-221.510885247941 -109.588514788964,-228.270643805406 -87.3045772259111,-232.294614119009 -46.4485209972234,-228.270643805406 -5.59246476853568,-216.353371787081 33.6935161316239,-197.000772144416 69.8996834890942,-170.956554428614 101.63465459698,-139.221583320728 127.678872312782,-103.015415963258 147.031471955448,-63.7294350630982 158.948743973773,-22.8733788344104 162.972714287376,17.9826773942774 158.948743973774,57.2686582944371 147.031471955449,93.4748256519074 127.678872312783,125.209796759793 101.634654596981,151.254014475596 69.8996834890953,170.606614118262 33.6935161316251,182.523886136587 -5.59246476853451,186.547856450189 -46.4485209972227)",
                            "LINESTRING(186.547856450189 -46.4485209972227,182.523886136587 -87.3045772259105,170.606614118262 -126.59055812607,151.254014475596 -162.79672548354,125.209796759794 -194.531696591426,93.4748256519081 -220.575914307228,65.3272038227373 -235.621131625452,36.2687622716732 -244.435913500765,-9.05803921416017 -248.900213788796,-54.3848406999935 -244.435913500765,-97.9697586242894 -231.214573193132,-138.137849033921 -209.744281559306,-173.34547474097 -180.850129866096,-202.239626434179 -145.642504159047,-221.510885247941 -109.588514788964,-228.270643805406 -87.3045772259111,-232.294614119009 -46.4485209972234,-228.270643805406 -5.59246476853568,-216.353371787081 33.6935161316239,-197.000772144416 69.8996834890942,-170.956554428614 101.63465459698,-139.221583320728 127.678872312782,-103.015415963258 147.031471955448,-63.7294350630982 158.948743973773,-22.8733788344104 162.972714287376,17.9826773942774 158.948743973774,57.2686582944371 147.031471955449,93.4748256519074 127.678872312783,125.209796759793 101.634654596981,151.254014475596 69.8996834890953,170.606614118262 33.6935161316251,182.523886136587 -5.59246476853451,186.547856450189 -46.4485209972227)",
                            "LINESTRING(186.547856450189 -46.4485209972227,182.523886136587 -87.3045772259105,170.606614118262 -126.59055812607,151.254014475596 -162.79672548354,125.209796759794 -194.531696591426,93.4748256519081 -220.575914307228,65.3272038227373 -235.621131625452,36.2687622716732 -244.435913500765,-9.05803921416017 -248.900213788796,-54.3848406999935 -244.435913500765,-97.9697586242894 -231.214573193132,-138.137849033921 -209.744281559306,-173.34547474097 -180.850129866096,-202.239626434179 -145.642504159047,-221.510885247941 -109.588514788964,-228.270643805406 -87.3045772259111,-232.294614119009 -46.4485209972234,-228.270643805406 -5.59246476853568,-216.353371787081 33.6935161316239,-197.000772144416 69.8996834890942,-170.956554428614 101.63465459698,-139.221583320728 127.678872312782,-103.015415963258 147.031471955448,-63.7294350630982 158.948743973773,-22.8733788344104 162.972714287376,17.9826773942774 158.948743973774,57.2686582944371 147.031471955449,93.4748256519074 127.678872312783,125.209796759793 101.634654596981,151.254014475596 69.8996834890953,170.606614118262 33.6935161316251,182.523886136587 -5.59246476853451,186.547856450189 -46.4485209972227)"),
                polygon = c("POLYGON((186.547856450189 -46.4485209972227,182.523886136587 -87.3045772259105,170.606614118262 -126.59055812607,151.254014475596 -162.79672548354,125.209796759794 -194.531696591426,93.4748256519081 -220.575914307228,65.3272038227373 -235.621131625452,36.2687622716732 -244.435913500765,-9.05803921416017 -248.900213788796,-54.3848406999935 -244.435913500765,-97.9697586242894 -231.214573193132,-138.137849033921 -209.744281559306,-173.34547474097 -180.850129866096,-202.239626434179 -145.642504159047,-221.510885247941 -109.588514788964,-228.270643805406 -87.3045772259111,-232.294614119009 -46.4485209972234,-228.270643805406 -5.59246476853568,-216.353371787081 33.6935161316239,-197.000772144416 69.8996834890942,-170.956554428614 101.63465459698,-139.221583320728 127.678872312782,-103.015415963258 147.031471955448,-63.7294350630982 158.948743973773,-22.8733788344104 162.972714287376,17.9826773942774 158.948743973774,57.2686582944371 147.031471955449,93.4748256519074 127.678872312783,125.209796759793 101.634654596981,151.254014475596 69.8996834890953,170.606614118262 33.6935161316251,182.523886136587 -5.59246476853451,186.547856450189 -46.4485209972227))", 
                            "POLYGON((186.547856450189 -46.4485209972227,182.523886136587 -87.3045772259105,170.606614118262 -126.59055812607,151.254014475596 -162.79672548354,125.209796759794 -194.531696591426,93.4748256519081 -220.575914307228,65.3272038227373 -235.621131625452,36.2687622716732 -244.435913500765,-9.05803921416017 -248.900213788796,-54.3848406999935 -244.435913500765,-97.9697586242894 -231.214573193132,-138.137849033921 -209.744281559306,-173.34547474097 -180.850129866096,-202.239626434179 -145.642504159047,-221.510885247941 -109.588514788964,-228.270643805406 -87.3045772259111,-232.294614119009 -46.4485209972234,-228.270643805406 -5.59246476853568,-216.353371787081 33.6935161316239,-197.000772144416 69.8996834890942,-170.956554428614 101.63465459698,-139.221583320728 127.678872312782,-103.015415963258 147.031471955448,-63.7294350630982 158.948743973773,-22.8733788344104 162.972714287376,17.9826773942774 158.948743973774,57.2686582944371 147.031471955449,93.4748256519074 127.678872312783,125.209796759793 101.634654596981,151.254014475596 69.8996834890953,170.606614118262 33.6935161316251,182.523886136587 -5.59246476853451,186.547856450189 -46.4485209972227))",
                            "POLYGON((186.547856450189 -46.4485209972227,182.523886136587 -87.3045772259105,170.606614118262 -126.59055812607,151.254014475596 -162.79672548354,125.209796759794 -194.531696591426,93.4748256519081 -220.575914307228,65.3272038227373 -235.621131625452,36.2687622716732 -244.435913500765,-9.05803921416017 -248.900213788796,-54.3848406999935 -244.435913500765,-97.9697586242894 -231.214573193132,-138.137849033921 -209.744281559306,-173.34547474097 -180.850129866096,-202.239626434179 -145.642504159047,-221.510885247941 -109.588514788964,-228.270643805406 -87.3045772259111,-232.294614119009 -46.4485209972234,-228.270643805406 -5.59246476853568,-216.353371787081 33.6935161316239,-197.000772144416 69.8996834890942,-170.956554428614 101.63465459698,-139.221583320728 127.678872312782,-103.015415963258 147.031471955448,-63.7294350630982 158.948743973773,-22.8733788344104 162.972714287376,17.9826773942774 158.948743973774,57.2686582944371 147.031471955449,93.4748256519074 127.678872312783,125.209796759793 101.634654596981,151.254014475596 69.8996834890953,170.606614118262 33.6935161316251,182.523886136587 -5.59246476853451,186.547856450189 -46.4485209972227))",
                            "POLYGON((186.547856450189 -46.4485209972227,182.523886136587 -87.3045772259105,170.606614118262 -126.59055812607,151.254014475596 -162.79672548354,125.209796759794 -194.531696591426,93.4748256519081 -220.575914307228,65.3272038227373 -235.621131625452,36.2687622716732 -244.435913500765,-9.05803921416017 -248.900213788796,-54.3848406999935 -244.435913500765,-97.9697586242894 -231.214573193132,-138.137849033921 -209.744281559306,-173.34547474097 -180.850129866096,-202.239626434179 -145.642504159047,-221.510885247941 -109.588514788964,-228.270643805406 -87.3045772259111,-232.294614119009 -46.4485209972234,-228.270643805406 -5.59246476853568,-216.353371787081 33.6935161316239,-197.000772144416 69.8996834890942,-170.956554428614 101.63465459698,-139.221583320728 127.678872312782,-103.015415963258 147.031471955448,-63.7294350630982 158.948743973773,-22.8733788344104 162.972714287376,17.9826773942774 158.948743973774,57.2686582944371 147.031471955449,93.4748256519074 127.678872312783,125.209796759793 101.634654596981,151.254014475596 69.8996834890953,170.606614118262 33.6935161316251,182.523886136587 -5.59246476853451,186.547856450189 -46.4485209972227))",
                            "POLYGON((186.547856450189 -46.4485209972227,182.523886136587 -87.3045772259105,170.606614118262 -126.59055812607,151.254014475596 -162.79672548354,125.209796759794 -194.531696591426,93.4748256519081 -220.575914307228,65.3272038227373 -235.621131625452,36.2687622716732 -244.435913500765,-9.05803921416017 -248.900213788796,-54.3848406999935 -244.435913500765,-97.9697586242894 -231.214573193132,-138.137849033921 -209.744281559306,-173.34547474097 -180.850129866096,-202.239626434179 -145.642504159047,-221.510885247941 -109.588514788964,-228.270643805406 -87.3045772259111,-232.294614119009 -46.4485209972234,-228.270643805406 -5.59246476853568,-216.353371787081 33.6935161316239,-197.000772144416 69.8996834890942,-170.956554428614 101.63465459698,-139.221583320728 127.678872312782,-103.015415963258 147.031471955448,-63.7294350630982 158.948743973773,-22.8733788344104 162.972714287376,17.9826773942774 158.948743973774,57.2686582944371 147.031471955449,93.4748256519074 127.678872312783,125.209796759793 101.634654596981,151.254014475596 69.8996834890953,170.606614118262 33.6935161316251,182.523886136587 -5.59246476853451,186.547856450189 -46.4485209972227))",
                            "POLYGON((186.547856450189 -46.4485209972227,182.523886136587 -87.3045772259105,170.606614118262 -126.59055812607,151.254014475596 -162.79672548354,125.209796759794 -194.531696591426,93.4748256519081 -220.575914307228,65.3272038227373 -235.621131625452,36.2687622716732 -244.435913500765,-9.05803921416017 -248.900213788796,-54.3848406999935 -244.435913500765,-97.9697586242894 -231.214573193132,-138.137849033921 -209.744281559306,-173.34547474097 -180.850129866096,-202.239626434179 -145.642504159047,-221.510885247941 -109.588514788964,-228.270643805406 -87.3045772259111,-232.294614119009 -46.4485209972234,-228.270643805406 -5.59246476853568,-216.353371787081 33.6935161316239,-197.000772144416 69.8996834890942,-170.956554428614 101.63465459698,-139.221583320728 127.678872312782,-103.015415963258 147.031471955448,-63.7294350630982 158.948743973773,-22.8733788344104 162.972714287376,17.9826773942774 158.948743973774,57.2686582944371 147.031471955449,93.4748256519074 127.678872312783,125.209796759793 101.634654596981,151.254014475596 69.8996834890953,170.606614118262 33.6935161316251,182.523886136587 -5.59246476853451,186.547856450189 -46.4485209972227))"), stringsAsFactors = F)

所有的点都不一样，线串都一样，多边形也一样（和线串一样，只是一个多边形而已）。

现在，我想使用ggplot 可视化这些几何图形。

我希望使用 ggplot 的“简单功能”方面（参见 geom_sf），但它似乎 ~~已被弃用或尚未实现。我确实看到了对 geom_sf 的引用，但它似乎~~仍在开发中......

~~geom_map 和 geom_polygon 都需要 x 和 y 变量。有没有一种从几何 WKT 对象中提取 x 和 y 坐标的快速方法？~~

【问题讨论】：

您需要ggplot2 的开发版本才能使用geom_sf，其余的您可以将data.frame 转换为sf，然后使用geom_sf。使用st_as_sf 转换例如st_as_sf(tmpdf, wkt = "polygon") 为多边形，st_as_sf(tmpdf, wkt = "linestr") 等
谢谢，正如您评论的那样，我想通了。这是很棒的新功能！
是的，sf 确实改变了游戏规则，喜欢它并迫不及待地想使用 stars 包来获得对栅格数据的类似支持。您可以使用 dbplyr 语法 github.com/r-dbi/DBI/issues/203 github.com/r-dbi/RPostgres/issues/86 直接支持 PostGIS
请注意geom_sf 显然忽略了scale_y_reverse() 转换。

标签： r ggplot2 postgis spatial

【解决方案1】：

如果您使用一些额外的库将 WKT 转换为 SpatialPoints/SpatialPolygons 并提取坐标，则使用 ggplot2（但不使用 geom_sf）绘制几何图形有点简单：

library(rgeos)
library(sp)

# read WKT points into spatial object
tmpdf$pts <- lapply(tmpdf$point, FUN = function(x) readWKT(x))

# extract point coordinates
tmpdf$ptx <- coordinates(tmpdf$pts)[c(T,F)]
tmpdf$pty <- coordinates(tmpdf$pts)[c(F,T)]

ggplot(tmpdf) + 
  geom_point(aes(x=ptx, y=pty))

虽然不清楚如何从多边形对象中提取坐标，但我能够做到的唯一方法似乎非常笨拙。一个问题是函数没有向量化，所以它们都需要用apply 函数包装。

# read WKT polygons into spatial object
tmpdf$pol <- lapply(tmpdf$polygon, FUN = function(x) readWKT(x))

# extract coordinates from the first polygon only
test <- tmpdf[1,"pol"]
test2 <- sapply(test, FUN=function(x) x@polygons)
test3 <- sapply(test2, FUN=function(x) x@Polygons)
test4 <- lapply(test3, FUN=function(x) x@coords)

ggplot() + 
  geom_point(data=tmpdf, aes(x=ptx, y=pty)) +
  geom_polygon(data=data.frame(test4[[1]]), aes(x=x, y=y), fill="transparent", color="blue")

以上仅适用，因为我知道每个多边形都是等价的。我必须做更多的工作来弄清楚如何为不同的多边形做到这一点。

**** 更新！

通过反复试验，我能够成功使用geom_sf。 this page 上的功能非常有用。

# install the dev version of ggplot2 (2.2.1.9000)
devtools::install_github("tidyverse/ggplot2")

# convert wkt to spatial (sf)
tmpdf$sppt <- st_as_sfc(tmpdf$point)
tmpdf$spls <- st_as_sfc(tmpdf$linestr)
tmpdf$sppg <- st_as_sfc(tmpdf$polygon) 

# regular plotting works
plot(tmpdf$sppt)
plot(tmpdf$spls)
plot(tmpdf$sppg)

# ggplot too!
ggplot(tmpdf) + 
  geom_sf(aes(geometry=sppt))

【讨论】：