从多边形列表创建空间多边形数据框 [英] Creating spatialpolygons dataframe from list of polygons
问题描述
我目前正在尝试根据多边形列表(用于生物多样性研究的研究区域)创建多边形shapefile.
I am currently trying to create a polygon shapefile from a list of polygons (study areas for biodiversity research).
当前，这些多边形以以下格式存储在列表中:
Currently these polygons are stored in a list in this format:
$SEW22
[,1] [,2]
[1,] 427260.4 5879458
[2,] 427161.4 5879472
[3,] 427175.0 5879571
[4,] 427273.9 5879557
[5,] 427260.4 5879458
$SEW23
[,1] [,2]
[1,] 418011.0 5867216
[2,] 417912.0 5867230
[3,] 417925.5 5867329
[4,] 418024.5 5867315
[5,] 418011.0 5867216
我尝试使用 writeOGR 将它们简单地写为shpfile，但是发生以下错误:
I tried to simply write them as shpfile with writeOGR but the following error occurs:
> #write polygons to shp
> filenameshp <- paste('Forestplots')
> layername <- paste('Forestplots')
> writeOGR(obj=forest, dsn = filenameshp,
+ layer=layername, driver="ESRI Shapefile", overwrite_layer = TRUE)
Error in writeOGR(obj = forest, dsn = filenameshp, layer = layername, :
inherits(obj, "Spatial") is not TRUE
我阅读了Barry Rowlingson撰写的这教程，以创建空间多边形和认为我应该先创建一个数据框并执行以下操作:
I read this tutorial by Barry Rowlingson to create spatialpolygons and thought I should probably first create a dataframe and did this:
forestm<-do.call(rbind,forest)
但是这没有返回您所能想象的有用的东西，而且它丢失了绘图的名称.
but this returned nothing useful as you can imagine, plus it lost the names of the plots.
由于我还是R语言的新手，所以我也尝试了许多其他方法，这些方法我无法完全判断，但没有一种方法能返回我希望的结果，因此我不愿使用这些随机方法....
As I am still new to R I also tried lots of different other approaches which sensefulness I could not fully judge but none returned what I hoped for and so I spare you with these random approaches.....
我期待着你的主张.
非常感谢
P.S.我还按照spacepolygons {sp} 程序包:
P.S. I also tried the following as described in the spatialpolygons{sp} package:
> Polygons(forest, ID)
Error in Polygons(forest, ID) : srl not a list of Polygon objects
推荐答案
You can follow the approach described in this answer: https://gis.stackexchange.com/questions/18311/instantiating-spatial-polygon-without-using-a-shapefile-in-r.
以下是将这种方法应用于您的案件的方法.首先，在您的示例数据中创建一个矩阵列表:
Here's how to apply the approach to your case. First, I create a list of matrices as in your sample data:
forest <- list(
"SEW22" = matrix(c(427260.4, 5879458, 427161.4, 5879472, 427175.0, 5879571, 427273.9, 5879557, 427260.4, 5879458),
nc = 2, byrow = TRUE),
"SEW23" = matrix(c(418011.0, 5867216, 417912.0, 5867230, 417925.5, 5867329, 418024.5, 5867315, 418011.0, 5867216),
nc = 2, byrow = TRUE)
)
现在
library(sp)
p <- lapply(forest, Polygon)
ps <- lapply(seq_along(p), function(i) Polygons(list(p[[i]]), ID = names(p)[i]))
sps <- SpatialPolygons(ps)
sps_df <- SpatialPolygonsDataFrame(sps, data.frame(x = rep(NA, length(p)), row.names = names(p)))
第一步，我们遍历矩阵列表，并对每个矩阵应用Polygon函数，以创建Polygon对象的列表.在第二步中，我们遍历此列表以创建Polygons对象，并将此对象中每个元素的ID设置为原始列表中的对应名称(例如"SEW22"，"SEW23").第三步创建一个SpatialPolygons对象.最后，我们创建一个SpatialPolygonsDataFrame对象.在这里，我有一个用NA填充的虚拟数据框(请注意，行名称必须与多边形ID对应).
In the first step, we iterate through the list of matrices and apply the Polygon function to each matrix to create a list of Polygon objects. In the second step, we iterate through this list to create a Polygons object, setting the ID of each element in this object to the corresponding name in the original list (e.g. "SEW22", "SEW23"). The third step creates a SpatialPolygons object. Finally, we create a SpatialPolygonsDataFrame object. Here I have a dummy dataframe populated with NAs (note that the row names must correspond to the polygon IDs).
最后，写入数据
rgdal::writeOGR(obj = sps_df,
dsn = "Forestplots",
layer = "Forestplots",
driver = "ESRI Shapefile",
overwrite_layer = TRUE)
这将在您的工作目录中创建一个新文件夹:
This creates a new folder in your working directory:
list.files()
# [1] "Forestplots"
list.files("Forestplots")
# [1] "Forestplots.dbf" "Forestplots.shp" "Forestplots.shx"
请咨询链接的答案以获取更多详细信息.
Consult the linked answer for more details.
这篇关于从多边形列表创建空间多边形数据框的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
