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[英]R | sf: I have points and 2 buffers around each point. How to combine the points into single units if larger buffer overlaps (but smaller does not)?
[英]R function for creating discs around each point in a pattern, then counting number of points in each disc [spatial]
我正在嘗試為模式中的每個點創建一個光盤; 每個圓盤將具有相同的半徑。 然后對於每個光盤,我想計算落在光盤內的點數。 每個模式有100-400點。 我已經編寫了代碼來做到這一點,但它很慢。 代碼如下。 我無法提供 shapefile 和點,因為這會非常困難,但如果需要,我可以創建一些虛擬數據。
W <- as.owin(shape)
#Converts created .shp file into a "window"
#in which everything is plotted and calculated
SPDF <- SpatialPointsDataFrame(P[,1:2], P)
#Converts data frame to spatial points data frame
SP <- as(SPDF, "SpatialPoints") #Converts SPDF to spatial points
SP1 <- as.ppp(coordinates(SP), W)
SP2 <- as.ppp(SP1)
attr(SP1, "rejects")
attr(SP2, "rejects")
aw <- area.owin(W) #Area, in pixels squared, of leaf window created earlier
#awm <- aw * (meas)^2 * 100 #Area window in millimeters squared
# Trichome_Density_Count-----------------------------------------------------------------------------------------------
TC <- nrow(P) #Counts number of rows in XY data points file,
#this is number of trichomes from ImageJ
TD <- TC/awm #Trichome density, trichomes per mm^2
#SPDF2 <- as.SpatialPoints.ppp(SP2)
#kg <- knn.graph(SPDF2, k = 1)
#Creates the lines connecting each NND pairwise connection
#dfkg <- data.frame(kg) #Converts lines into a data frame
#dfkgl <- dfkg$length
meanlength <- 78
discstest <- discs(SP2, radii = meanlength,
separate = TRUE, mask = FALSE, trim = FALSE,
delta = NULL, npoly=NULL)
#Function creates discs for each trichome
#Using nearest neighbor lengths as radii
#NEED TO ADD CLIPPING
ratiolist <- c()
for (i in 1:length(discstest)) {
ow2sp <- owin2SP(discstest[[i]])
leafsp <- owin2SP(W)
tic("gIntersection")
intersect <- rgeos::gIntersection(ow2sp, leafsp)
Sys.sleep(1)
toc()
tic("over")
res <- as.data.frame(sp::over(SP, intersect, returnList = FALSE))
Sys.sleep(1)
toc()
res[is.na(res)] <- 0
newowin <- as.owin(intersect)
circarea <- area.owin(newowin)
trichactual <- sum(res)
trichexpect <- (TC / aw) * circarea
ratio <- trichactual / trichexpect
ratiolist[[i]] <- ratio
}
如果我理解正確,您想遍歷每個點並檢查有多少點落在以該點為中心的半徑為 R 的圓盤內。 這在 spatstat 中使用closepaircounts
函數非常有效地完成:
closepaircounts(SP2, r = meanlength)
這只是返回一個向量,該向量包含SP2
每個點的半徑為r
的圓盤中包含的點數。
我剛剛嘗試了 100,000 個點,其中每個點在它周圍的光盤上平均有近 3000 個其他點,在我的筆記本電腦上花了 8 秒。 如果你有更多的點,或者特別是如果圓盤半徑太大以至於每個圓盤包含更多的點,計算這個可能會變得非常慢。
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