Terra 中的负缓冲区对于复杂的多多边形有意想不到的结果

Question

本周我一直在使用

buffer

中的

terra

功能。我正在应用负缓冲区来获得我的研究区域内的区域。我最初的输入多边形创建了多个奇怪的结果并使 R 崩溃了几次。我找到了以下解决方案，但我怀疑它们是解决方法，并且可能有更好的方法来解决它们。

• 问题编号1：聚合多边形创建一个奇数多边形，即 在原始多边形之外

• 解决方案：在原始文件上运行

  disagg

• 问题编号2：带有孔（或内环）的多边形有一个在孔/环外部创建的缓冲区，可以超出外多边形

• 解决方案：在原始文件上运行

  fillHoles

• 问题编号3：R 经常崩溃（尽管不规律）

• 解决方案：使用非投影坐标系代替原来的坐标系 输入文件的预计crs

我上周更新了

terra

，并在 Windows 11 上运行版本 1.7-55。我有第 13 代 Intel(R) Core(TM) i7-1355U 1.70 GHz 和 16GB RAM。

library(terra)

issue 1 : aggregated polygons create an odd polygon that is outside the original polygons

#three-polygon spatVector which generates odd inset buffer
p1<-vect("POLYGON ((-66.940374 45.008097, -66.971762 45, -66.986546 45.008447, -66.940267 45.026992, -66.940374 45.008097))")                                                                                                                                                                                                              
p2<-vect("POLYGON ((-66.828 45.032592, -66.829 45.035, -66.824 45.031, -66.8301 45.0275, -66.834 45.027, -66.828 45.032592))")                                                                                                                                                                                 
p3<-vect("POLYGON ((-67 46, -66.2 46, -66.2 45.65, -66.37 45.45, -66.37 45.105, -66.459 45.05, -66.46 45.17,
-66.78 45.04, -66.76 45.12, -66.89 45.04, -66.916 45.11, -66.89 45.1, -66.82 45.127, -66.96 45.19,
-67 45.15, -67 46))")

wkt.p<-rbind(p1, p2, p3)
crs(wkt.p)<-"+proj=longlat +datum=WGS84"

hol_buff<-buffer(aggregate(wkt.p), -2000)
plot(wkt.p, ylim=c(45, 46))
plot(hol_buff, add=T, col="green")

#dissaggreated polygons do not create odd inset
hol_buff<-buffer(wkt.p, -2000)
plot(hol_buff, add=T, col="red")

#three-polygon spatVector which does NOT generates odd inset buffer (upper limit of p3 changed from 46 to 45.8)
p1<-vect("POLYGON ((-66.940374 45.008097, -66.971762 45, -66.986546 45.008447, -66.940267 45.026992, -66.940374 45.008097))")                                                                                                                                                                                                              
p2<-vect("POLYGON ((-66.828 45.032592, -66.829 45.035, -66.824 45.031, -66.8301 45.0275, -66.834 45.027, -66.828 45.032592))")                                                                                                                                                                                 
p3<-vect("POLYGON ((-67 45.8, -66.2 45.8, -66.2 45.65, -66.37 45.45, -66.37 45.105, -66.459 45.05, -66.46 45.17,
-66.78 45.04, -66.76 45.12, -66.89 45.04, -66.916 45.11, -66.89 45.1, -66.82 45.127, -66.96 45.19,
-67 45.15, -67 45.8))")

wkt.p<-rbind(p1, p2, p3)
crs(wkt.p)<-"+proj=longlat +datum=WGS84"

hol_buff<-buffer(aggregate(wkt.p), -2000)
plot(wkt.p, ylim=c(45, 46))
plot(hol_buff, add=T, col="blue")

#issue no 2 : holes within polygons leads to negative buffer that are outside the polygon boundary


par(mfrow=c(1,2))
#polygon with inner ring
wkt.y<-"POLYGON ((-66.902 45.013, -66.901 45.01, -66.906 45.0114,  -66.9045 45.0155, -66.902 45.0155, -66.902 45.013),
(-66.903371 45.012734, -66.903372 45.012914, -66.903626 45.012913, -66.903624 45.012733, -66.903371 45.012734))"
y<-vect(wkt.y,crs="+proj=longlat +datum=WGS84")
plot(y, main="terra output")
plot(buffer(y, -40), add=T, col="red")

#polygon without inner ring
wkt.w<-"POLYGON ((-66.902 45.013, -66.901 45.01, -66.906 45.0114,  -66.9045 45.0155, -66.902 45.0155, -66.902 45.013))"
w<-vect(wkt.w,crs="+proj=longlat +datum=WGS84")
plot(y, main="desired output")
plot(buffer(w, -40), add=T, col="red")#negative buffer using the simple polygon that shows the desired buffered polygon
plot(y, add=T)#hypothetical input
#removing the inner ring can be done by using fillHoles
w2<-fillHoles(y)


#polygon with inner ring at edge
par(mfrow=c(1,2))
wkt.y<-"POLYGON ((-66.902 45.012,  -66.906 45.0114,  -66.906 45.0155, -66.902 45.0155, -66.902 45.012),
(-66.903371 45.012734, -66.903372 45.012914, -66.903626 45.012913, -66.903624 45.012733, -66.903371 45.012734))"
y<-vect(wkt.y,crs="+proj=longlat +datum=WGS84")
#plot(buffer(y, -200), col="red", )
plot(y, xlim=c(-66.907, -66.901), ylim=c(45.01, 45.017), main="terra output")
plot(buffer(y, -200), add=T, col="red", border="forestgreen", lwd=2)
plot(y, add=T)#overlay original polygon

#polygon without inner ring
wkt.w<-"POLYGON ((-66.902 45.012,  -66.906 45.0114,  -66.906 45.0155, -66.902 45.0155, -66.902 45.012))"
w<-vect(wkt.w,crs="+proj=longlat +datum=WGS84")
plot(y, main="desired output")
plot(buffer(w, -200), add=T, col="red")#negative buffer using the simple polygon that shows the desired buffered polygon
plot(y, add=T)#hypothetical input

Answer 1

像这样报告问题的更好地方是 terra github 站点。

如果您不希望孔在负缓冲中增长，那么您可以先将它们移除，就像您所做的那样。但可以添加替代选项，例如缩小孔。

否则，我认为您所报告的问题已在 terra 版本 1.7-63 中得到修复。这是目前的开发版本。你可以安装它

install.packages('terra', repos='https://rspatial.r-universe.dev')