gSimplify 不简化 R 中的 shapefile [英] gSimplify not simplifying shapefile in R

问题描述

我无法在 R 中简化 shapefile

I'm unable to simplify a shapefile in R

来自此处的形状文件:https://geoportal.statistics.gov.uk/Docs/Boundaries/Local_authority_district_(GB)_2014_Boundaries_(Generalised_Clipped).zip

library(tmap)
library(maptools)
library(ggmap)

England <- readOGR(dsn = "...")

#works fine
print(qtm(England, "LAD14CD", borders = NA, fill.title = "A-Level" )) 

# simplify the polygons
England<-gSimplify(England,tol=0.01, topologyPreserve=TRUE)

print(qtm(England, "LAD14CD", borders = NA, fill.title = "A-Level" )) 

给出错误:

Error in process_fill(data, g$tm_fill, gborders, gt, gf, z = z + which(plot.order ==  : 
Fill argument neither colors nor valid variable name(s)

如果您查看 UK 数据对象，您会发现它已从大空间多边形数据帧更改为大空间多边形并删除了 @data

If you look at the UK dataobject you can see that it has changed from a Large Spatial polygonDataFrame to Large Spatial Polygons and dropped the @data

相反，如果您尝试仅简化 Shapefile 中的多边形:

Instead, if you try to only simplify the polygons in the Shapefile:

England@polygons<-gSimplify(England@polygons,tol=0.01, topologyPreserve=TRUE)

它说:

Error in gSimplify(England@polygons, tol = 0.01, topologyPreserve = TRUE) : 
cannot get a slot ("proj4string") from an object of type "list"

如何简化 shapefile 中的多边形?

How can I simplify the polygons from a shapefile?

推荐答案

gSimplify 返回的只是几何图形，而不是属性，所以你必须构造一个新的 SpatialPolygonsDataFrame代码>使用简化的几何图形和原始的属性数据:

The return from gSimplify is just the geometry, not the attributes, so you have to construct a new SpatialPolygonsDataFrame with the simplified geometry and the attribute data from the original:

> England2 <-gSimplify(England,tol=0.01, topologyPreserve=TRUE)
> England3 = SpatialPolygonsDataFrame(England2, data=England@data)

我认为多边形的顺序是相同的，除非任何东西都被简化了.检查 length(England2) 与 England 的行数相同，或匹配 ID 上的行.

I think the polygons are guaranteed to be in the same order, unless anything has been simplified away. Check length(England2) has the same number of rows as England, or match up the rows on an ID.

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