r语言 - sf和星星:多边形分类光栅

Question

我想画栅格线(l)只是为了"目标"。不考虑NA值的x栅格分类。我试着做:

# 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，不工作。拜托，能帮帮忙吗?

提前感谢，

亚历山大

Answer 1

您的脚本有几个错误，首先，st_contour指示它与字符类型不兼容(指"target")您在光栅中设置的字符串)。其次，我建议使用st_contour中的break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。我对你的代码做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)