感謝來自this網站一些靈感，我的工作了一個功能輪廓線轉換爲填充的輪廓。它設置爲處理柵格對象並返回一個SpatialPolygonsDataFrame。
raster2contourPolys <- function(r, levels = NULL) {
## set-up levels
levels <- sort(levels)
plevels <- c(min(values(r), na.rm=TRUE), levels, max(values(r), na.rm=TRUE)) # pad with raster range
llevels <- paste(plevels[-length(plevels)], plevels[-1], sep=" - ")
llevels[1] <- paste("<", min(levels))
llevels[length(llevels)] <- paste(">", max(levels))
## convert raster object to matrix so it can be fed into contourLines
xmin <- extent(r)@xmin
xmax <- extent(r)@xmax
ymin <- extent(r)@ymin
ymax <- extent(r)@ymax
rx <- seq(xmin, xmax, length.out=ncol(r))
ry <- seq(ymin, ymax, length.out=nrow(r))
rz <- t(as.matrix(r))
rz <- rz[,ncol(rz):1] # reshape
## get contour lines and convert to SpatialLinesDataFrame
cat("Converting to contour lines...\n")
cl <- contourLines(rx,ry,rz,levels=levels)
cl <- ContourLines2SLDF(cl)
## extract coordinates to generate overall boundary polygon
xy <- coordinates(r)[which(!is.na(values(r))),]
i <- chull(xy)
b <- xy[c(i,i[1]),]
b <- SpatialPolygons(list(Polygons(list(Polygon(b, hole = FALSE)), "1")))
## add buffer around lines and cut boundary polygon
cat("Converting contour lines to polygons...\n")
bcl <- gBuffer(cl, width = 0.0001) # add small buffer so it cuts bounding poly
cp <- gDifference(b, bcl)
## restructure and make polygon number the ID
polys <- list()
for(j in seq_along([email protected][[1]]@Polygons)) {
polys[[j]] <- Polygons(list([email protected][[1]]@Polygons[[j]]),j)
}
cp <- SpatialPolygons(polys)
cp <- SpatialPolygonsDataFrame(cp, data.frame(id=seq_along(cp)))
## cut the raster by levels
rc <- cut(r, breaks=plevels)
## loop through each polygon, create internal buffer, select points and define overlap with raster
cat("Adding attributes to polygons...\n")
l <- character(length(cp))
for(j in seq_along(cp)) {
p <- cp[cp$id==j,]
bp <- gBuffer(p, width = -max(res(r))) # use a negative buffer to obtain internal points
if(!is.null(bp)) {
xy <- SpatialPoints(coordinates([email protected][[1]]@Polygons[[1]]))[1]
l[j] <- llevels[extract(rc,xy)]
}
else {
xy <- coordinates(gCentroid(p)) # buffer will not be calculated for smaller polygons, so grab centroid
l[j] <- llevels[extract(rc,xy)]
}
}
## assign level to each polygon
cp$level <- factor(l, levels=llevels)
cp$min <- plevels[-length(plevels)][cp$level]
cp$max <- plevels[-1][cp$level]
cp <- cp[!is.na(cp$level),] # discard small polygons that did not capture a raster point
df <- unique([email protected][,c("level","min","max")]) # to be used after holes are defined
df <- df[order(df$min),]
row.names(df) <- df$level
llevels <- df$level
## define depressions in higher levels (ie holes)
cat("Defining holes...\n")
spolys <- list()
p <- cp[cp$level==llevels[1],] # add deepest layer
p <- gUnaryUnion(p)
spolys[[1]] <- Polygons([email protected][[1]]@Polygons, ID=llevels[1])
for(i in seq(length(llevels)-1)) {
p1 <- cp[cp$level==llevels[i+1],] # upper layer
p2 <- cp[cp$level==llevels[i],] # lower layer
x <- numeric(length(p2)) # grab one point from each of the deeper polygons
y <- numeric(length(p2))
id <- numeric(length(p2))
for(j in seq_along(p2)) {
xy <- coordinates([email protected][[j]]@Polygons[[1]])[1,]
x[j] <- xy[1]; y[j] <- xy[2]
id[j] <- as.numeric([email protected][[j]]@ID)
}
xy <- SpatialPointsDataFrame(cbind(x,y), data.frame(id=id))
holes <- over(xy, p1)$id
holes <- xy$id[which(!is.na(holes))]
if(length(holes)>0) {
p2 <- p2[p2$id %in% holes,] # keep the polygons over the shallower polygon
p1 <- gUnaryUnion(p1) # simplify each group of polygons
p2 <- gUnaryUnion(p2)
p <- gDifference(p1, p2) # cut holes in p1
} else { p <- gUnaryUnion(p1) }
spolys[[i+1]] <- Polygons([email protected][[1]]@Polygons, ID=llevels[i+1]) # add level
}
cp <- SpatialPolygons(spolys, pO=seq_along(llevels), proj4string=CRS(proj4string(r))) # compile into final object
cp <- SpatialPolygonsDataFrame(cp, df)
cat("Done!")
cp
}
它可能存在一些低效率，但它在我使用海底測量數據進行的測試中運行良好。下面是使用了火山的數據爲例：
r <- raster(t(volcano))
l <- seq(100,200,by=10)
cp <- raster2contourPolys(r, levels=l)
cols <- terrain.colors(length(cp))
plot(cp, col=cols, border=cols, axes=TRUE, xaxs="i", yaxs="i")
contour(r, levels=l, add=TRUE)
box()
不能找到一個完整的解決方案，但使用'輪廓（火山，加= TRUE）'已經解決了你的部分問題或？ –
謝謝@thijsvandenbergh - 我希望得到實際的多邊形，以嘗試將這些投影到另一個網格上。 –
，我沒有得到，但這可能是有幫助的：[link]（http://stackoverflow.com/questions/12849623/in-r-how-does-one-place-multiple-filled-contour-plots-in-一個單一設備） –