如何将轮廓线转换为填充轮廓？
有人知道一种方法可以转换contourLines多边形的输出，以便绘制为填充的轮廓，就像使用filled.contours一样。是否有关于如何绘制多边形以便查看所有可用级别的顺序？以下是一段不起作用的示例代码：
#typical plot
filled.contour(volcano, color.palette = terrain.colors)
#try
cont <- contourLines(volcano)
fun <- function(x) x$level
LEVS <- sort(unique(unlist(lapply(cont, fun))))
COLS <- terrain.colors(length(LEVS))
contour(volcano)
for(i in seq(cont)){
COLNUM <- match(cont[[i]]$level, LEVS)
polygon(cont[[i]], col=COLS[COLNUM], border="NA")
}
contour(volcano, add=TRUE)
3 个答案:
答案 0 :(得分：7)
使用raster包（调用rgeos和sp）的解决方案。输出为SpatialPolygonsDataFrame，将覆盖网格中的每个值：
library('raster')
rr <- raster(t(volcano))
rc <- cut(rr, breaks= 10)
pols <- rasterToPolygons(rc, dissolve=T)
spplot(pols)
Here's a discussion将向您展示如何简化（'美化'）生成的多边形。
答案 1 :(得分：5)
感谢来自this网站的一些灵感，我编写了一个功能，将轮廓线转换为填充轮廓。它设置为处理栅格对象并返回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(cp@polygons[[1]]@Polygons)) {
polys[[j]] <- Polygons(list(cp@polygons[[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$id==j,]
bp <- gBuffer(p, width = -max(res(r))) # use a negative buffer to obtain internal points
if(!is.null(bp)) {
xy <- SpatialPoints(coordinates(bp@polygons[[1]]@Polygons[[1]]))[1]
l[j] <- llevels[extract(rc,xy)]
}
else {
xy <- coordinates(gCentroid(p)) # buffer will not be calculated for smaller polygons, so grab centroid
l[j] <- llevels[extract(rc,xy)]
}
}
## assign level to each polygon
cp$level <- factor(l, levels=llevels)
cp$min <- plevels[-length(plevels)][cp$level]
cp$max <- plevels[-1][cp$level]
cp <- cp[!is.na(cp$level),] # discard small polygons that did not capture a raster point
df <- unique(cp@data[,c("level","min","max")]) # to be used after holes are defined
df <- df[order(df$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$level==llevels[1],] # add deepest layer
p <- gUnaryUnion(p)
spolys[[1]] <- Polygons(p@polygons[[1]]@Polygons, ID=llevels[1])
for(i in seq(length(llevels)-1)) {
p1 <- cp[cp$level==llevels[i+1],] # upper layer
p2 <- cp[cp$level==llevels[i],] # lower layer
x <- numeric(length(p2)) # grab one point from each of the deeper polygons
y <- numeric(length(p2))
id <- numeric(length(p2))
for(j in seq_along(p2)) {
xy <- coordinates(p2@polygons[[j]]@Polygons[[1]])[1,]
x[j] <- xy[1]; y[j] <- xy[2]
id[j] <- as.numeric(p2@polygons[[j]]@ID)
}
xy <- SpatialPointsDataFrame(cbind(x,y), data.frame(id=id))
holes <- over(xy, p1)$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(p@polygons[[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，但它在我使用测深数据进行的测试中运行良好。以下是使用火山数据的示例：
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()
答案 2 :(得分：2)
在Paul Regular的优秀作品的基础上，这是一个应该确保独有多边形的版本（即没有重叠）。
我为 fairy dust 添加了一个新参数fd来解决我发现使用UTM类型坐标的问题。基本上我理解算法的工作原理是从轮廓线中采样横向点，以确定哪个边是 in 多边形。样本点与线的距离如果最终出现在例如线上会产生问题。在另一个轮廓后面因此，如果您生成的多边形看起来不对，请尝试将fd设置为值10 ^±n，直到它看起来非常错误或正确...
raster2contourPolys <- function(r, levels = NULL, fd = 1) {
## set-up levels
levels <- sort(levels)
plevels <- c(min(values(r)-1, na.rm=TRUE), levels, max(values(r)+1, 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")
cl0 <- contourLines(rx, ry, rz, levels = levels)
cl <- ContourLines2SLDF(cl0)
## 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 = fd*diff(bbox(r)[1,])/3600000) # 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(cp@polygons[[1]]@Polygons)) {
polys[[j]] <- Polygons(list(cp@polygons[[1]]@Polygons[[j]]),j)
}
cp <- SpatialPolygons(polys)
cp <- SpatialPolygonsDataFrame(cp, data.frame(id=seq_along(cp)))
# group by elev (replicate ids)
# ids = sapply(slot(cl, "lines"), slot, "ID")
# lens = sapply(1:length(cl), function(i) length(cl[i,]@lines[[1]]@Lines))
## 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$id==j,]
bp <- gBuffer(p, width = -max(res(r))) # use a negative buffer to obtain internal points
if(!is.null(bp)) {
xy <- SpatialPoints(coordinates(bp@polygons[[1]]@Polygons[[1]]))[1]
l[j] <- llevels[raster::extract(rc,xy)]
}
else {
xy <- coordinates(gCentroid(p)) # buffer will not be calculated for smaller polygons, so grab centroid
l[j] <- llevels[raster::extract(rc,xy)]
}
}
## assign level to each polygon
cp$level <- factor(l, levels=llevels)
cp$min <- plevels[-length(plevels)][cp$level]
cp$max <- plevels[-1][cp$level]
cp <- cp[!is.na(cp$level),] # discard small polygons that did not capture a raster point
df <- unique(cp@data[,c("level","min","max")]) # to be used after holes are defined
df <- df[order(df$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$level==llevels[1],] # add deepest layer
p <- gUnaryUnion(p)
spolys[[1]] <- Polygons(p@polygons[[1]]@Polygons, ID=llevels[1])
for(i in seq(length(llevels)-1)) {
p1 <- cp[cp$level==llevels[i+1],] # upper layer
p2 <- cp[cp$level==llevels[i],] # lower layer
x <- numeric(length(p2)) # grab one point from each of the deeper polygons
y <- numeric(length(p2))
id <- numeric(length(p2))
for(j in seq_along(p2)) {
xy <- coordinates(p2@polygons[[j]]@Polygons[[1]])[1,]
x[j] <- xy[1]; y[j] <- xy[2]
id[j] <- as.numeric(p2@polygons[[j]]@ID)
}
xy <- SpatialPointsDataFrame(cbind(x,y), data.frame(id=id))
holes <- over(xy, p1)$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(p@polygons[[1]]@Polygons, ID=llevels[i+1]) # add level
}
cp <- SpatialPolygons(spolys, pO=seq_along(llevels), proj4string=CRS(proj4string(r))) # compile into final object
## make polygons exclusive (i.e. no overlapping)
cpx = gDifference(cp[1,], cp[2,], id=cp[1,]@polygons[[1]]@ID)
for(i in 2:(length(cp)-1)) cpx = spRbind(cpx, gDifference(cp[i,], cp[i+1,], id=cp[i,]@polygons[[1]]@ID))
cp = spRbind(cpx, cp[length(cp),])
## it's a wrap
cp <- SpatialPolygonsDataFrame(cp, df)
cat("Done!")
cp
}
相关问题
最新问题
- 我写了这段代码，但我无法理解我的错误
- 我无法从一个代码实例的列表中删除 None 值，但我可以在另一个实例中。为什么它适用于一个细分市场而不适用于另一个细分市场？
- 是否有可能使 loadstring 不可能等于打印？卢阿
- java中的random.expovariate()
- Appscript 通过会议在 Google 日历中发送电子邮件和创建活动
- 为什么我的 Onclick 箭头功能在 React 中不起作用？
- 在此代码中是否有使用“this”的替代方法？
- 在 SQL Server 和 PostgreSQL 上查询，我如何从第一个表获得第二个表的可视化
- 每千个数字得到
- 更新了城市边界 KML 文件的来源？