sf 和星星：多边形化分类栅格

Question

我只想为 x 栅格中的“目标”分类绘制栅格轮廓 (l)，而不考虑 NA 值。我尝试做：

# Packages
library(stars)
library(sf)

#Vectorizing a raster object to an sf object
tif = system.file("tif/L7_ETMs.tif", package = "stars")
x = read_stars(tif)[, 1:50, 1:50, 1:2]
x[[1]] = round(x[[1]]/5)
x[[1]] = ifelse(x[[1]]<10,NA,"target")
str(x[[1]])

#Polygonizing
l =  st_contour(x)
plot(l[1])
Error in CPL_write_gdal(mat, file, driver, options, type, dims, from,  : 
  Not compatible with requested type: [type=character; target=double].

但是，不起作用。请问有什么帮助吗？

提前致谢，

亚历山大

Answer 1

您的脚本有几个错误，首先，st_contour 表明它与字符类型不兼容（指的是您在光栅中设置的“目标”字符串）。其次，我建议在 st_contour 中使用 breaks 参数来设置您希望获得轮廓的目标值。此外，您可能希望使用 x[rule] <- NA 来屏蔽栅格中的某些值。我对您的代码进行了其他可能有帮助的修改：

# Let's stay with only the first band, indicated in the final dimension
x = read_stars(tif)[, 1:50, 1:50, 1]
x = round(x/5)
# Calculate the min and max of the raster values
purrr::map(x, min)
# 10
purrr::map(x, max)
# 28
# Mask values lower than 10
# However, this does not make any change, because the lowest value is 10
x[x<10] <- NA
# Take a look at the image
plot(x)

# Obtain the contours
l =  st_contour(x, 
                # Remove NA
                na.rm = T,
                # Obtain contour lines instead of polygons
                contour_lines = TRUE,
                # raster values at which to draw contour levels
                breaks = 12)
# Plot the contours
plot(l)

sf 和星星：多边形化分类栅格

sf and stars: polygonize categorical raster

r

raster

sf

r-stars