在 R 中执行 gCentroid 时出错

Question

我无法从 R 中的多边形获取质心。令人困惑的一点是，它过去可以工作，但突然停止工作了！这是一段代码：

polygon.centroids <- SpatialPointsDataFrame(gCentroid(polygon, byid = TRUE), 
                                      polygon@data, match.ID = FALSE)

我还可以确认多边形数据的 proj4string 已经存在，如下所示：

proj4string:    +proj=utm +zone=55 +south +ellps=GRS80 +units=m +no_defs

我在执行质心代码时得到的错误消息如下：

   Error in TopologyFunc(spgeom, id, byid, "rgeos_getcentroid") : 
  no slot of name "proj4string" for this object of class "sf"

知道发生了什么事吗？如前所述，此代码过去运行良好。

谢谢

Answer 1

使用as() function from the methods package to convert your sf object to a SpatialPolygonsDataFrame object - as mentioned in Reading, Writing and Converting Simple Features。

在这里，我使用 City of Chicago's 77 community areas 中的多边形来重现此建议。

更新

不是为了计算质心而转换整个 sf 对象，您可以在 gCentroid().

内部进行转换

# load neccessary packages
library( sf )
library( rgeos )

# load data
comarea606 <-
    read_sf( "https://data.cityofchicago.org/api/geospatial/cauq-8yn6?method=export&format=GeoJSON" )

# find the centroid of each polygon
gCentroid( spgeom = comarea606 )
# Error in TopologyFunc(spgeom, id, byid, "rgeos_getcentroid") : 
#     no slot of name "proj4string" for this object of class "sf"

# convert from sf
# to spatial polygon data frame
# to find the centroid of each polygon
centroids <- 
    gCentroid( 
        spgeom = methods::as( object = comarea606, Class = "Spatial" )
        , byid = TRUE 
        )

# view results
centroids
# SpatialPoints:
#     x        y
# 1  -87.61868 41.83512
# 2  -87.60322 41.82375
# 3  -87.63242 41.80909
# 4  -87.61786 41.81295
# 5  -87.59618 41.80892
# 6  -87.68752 41.97517
# 7  -87.61793 41.79236
# 8  -87.59231 41.79409
# 9  -87.59493 41.77888
# 10 -87.67017 42.00962
# 11 -87.77117 41.97883
# 12 -87.75836 41.99393
# 13 -87.72358 41.98364
# 14 -87.72156 41.96807
# 15 -87.76340 41.95403
# 16 -87.72345 41.95358
# 17 -87.80602 41.94651
# 18 -87.79803 41.92930
# 19 -87.76550 41.92726
# 20 -87.69501 42.00157
# 21 -87.73474 41.92435
# 22 -87.71121 41.93867
# 23 -87.69916 41.92276
# 24 -87.72092 41.90007
# 25 -87.67636 41.90121
# 26 -87.76311 41.89410
# 27 -87.73023 41.87859
# 28 -87.70590 41.87891
# 29 -87.66352 41.87401
# 30 -87.71722 41.86019
# 31 -87.65588 41.96581
# 32 -87.71400 41.83909
# 33 -87.66757 41.85027
# 34 -87.62033 41.85718
# 35 -87.63397 41.84208
# 36 -87.80345 41.98524
# 37 -87.63331 41.89960
# 38 -87.62519 41.87887
# 39 -87.57278 41.76158
# 40 -87.61597 41.74021
# 41 -87.58635 41.74420
# 42 -87.55143 41.74124
# 43 -87.59648 41.72818
# 44 -87.57272 41.72968
# 45 -87.62337 41.70659
# 46 -87.68384 41.94779
# 47 -87.59825 41.70613
# 48 -87.57006 41.69064
# 49 -87.53490 41.70731
# 50 -87.63574 41.67382
# 51 -87.60285 41.66014
# 52 -87.54658 41.66053
# 53 -87.76424 41.79619
# 54 -87.72636 41.81088
# 55 -87.69886 41.81737
# 56 -87.67250 41.82992
# 57 -87.65600 41.94423
# 58 -87.64879 41.83615
# 59 -87.65917 41.80902
# 60 -87.72421 41.79298
# 61 -87.69644 41.79543
# 62 -87.76851 41.77958
# 63 -87.72693 41.76978
# 64 -87.69567 41.77185
# 65 -87.66660 41.77593
# 66 -87.64250 41.77720
# 67 -87.61613 41.76325
# 68 -87.64949 41.92269
# 69 -87.70837 41.74576
# 70 -87.65631 41.74421
# 71 -87.67508 41.71315
# 72 -87.64890 41.71749
# 73 -87.71319 41.69488
# 74 -87.66905 41.68973
# 75 -87.89370 41.97568
# 76 -87.66342 41.98671
# 77 -87.81378 42.00761
# Coordinate Reference System (CRS) arguments: +proj=longlat
# +datum=WGS84 +no_defs +ellps=WGS84 +towgs84=0,0,0 

# end of script #

在 R 中执行 gCentroid 时出错

Error whilst performing gCentroid in R

r

polygon

centroid

rgeo-shapefile