SF对象CRS转换异常及坐标系匹配问题求助

Hey there, let's break down and fix these CRS problems step by step:

1. Repair the sf object's missing SRID and incomplete CRS #

When you converted your SpatialLinesDataFrame to sf with st_as_sf(roads, crs = 27700), you might have overwritten the full, official CRS definition that was already present in the original spatial object. Instead, use st_set_crs() with the EPSG code to load the complete, standardized CRS for EPSG:27700 (which includes the datum=OSGB36 info you're missing):

# Set the correct CRS using the EPSG code
roads <- st_set_crs(roads, 27700)

# Verify the fix
st_crs(roads)

This should now show epsg (SRID): 27700 along with the full proj4string including the datum details.

2. Fix the st_transform error #

The error cannot create a crs from an object of class CRS happens because st_transform() expects an sf-compatible CRS object (from st_crs()), not the sp-style CRS object returned by crs(raster). You have two simple fixes here:

Option 1: Convert the raster's CRS to an sf-compatible object #

# Get the raster's CRS in sf format
target_crs <- st_crs(crs(raster))

# Transform the roads sf object
roads <- st_transform(roads, target_crs)

Option 2: Use the proj4 string directly from the raster #

# Extract the proj4 string as a character
target_proj <- as.character(crs(raster))

# Transform using the proj4 string
roads <- st_transform(roads, target_proj)

3. Verify the transformation #

After running either option, check that the CRS matches your raster:

# Check roads CRS
st_crs(roads)

# Compare to raster CRS
crs(raster)

They should now align, and you can proceed with extracting values from your raster.

内容的提问来源于stack exchange，提问作者TheRealJimShady