I am updating code from rgdal to use the sf package.
I have a SpatialPolygonsDataFrame that I need to project.
In rgdal I used proj4string(). With sf, I tried to use st_crs():
library(sf)
ext <- extent(c(0, 20, 0, 20))
r <- raster(ext, res=1)
r[] = 1:ncell(r)
# convert the raster to polygon:
Output_Shapefile <- rasterToPolygons(r)
prj <- "+proj=eqdc +lat_0=17.8333333333333 +lon_0=-66.4333333333333 +lat_1=18.4333333333333 +lat_2=18.0333333333333 +x_0=200000 +y_0=200000 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs"
#project:
# proj4string(Output_Shapefile) <- prj
st_crs(Output_Shapefile) <- prj
Here is the error I am getting:
Error in UseMethod("st_crs<-") :
no applicable method for 'st_crs<-' applied to an object of class "c('SpatialPolygonsDataFrame', 'SpatialPolygons', 'Spatial', 'SpatialVector')"
First of all, consider working completely with sf and avoid the use of sp as sp is in maintenance mode right now.
Solution is to convert the SpatialPolygonsDataFrame to sf, assign the crs and back to SpatialPolygonsDataFrame:
library(sf)
#> Linking to GEOS 3.12.1, GDAL 3.8.4, PROJ 9.3.1; sf_use_s2() is TRUE
library(raster)
#> Cargando paquete requerido: sp
ext <- extent(c(0, 20, 0, 20))
r <- raster(ext, res = 1)
r[] <- 1:ncell(r)
# convert the raster to polygon:
Output_Shapefile <- rasterToPolygons(r)
prj <- "+proj=eqdc +lat_0=17.8333333333333 +lon_0=-66.4333333333333 +lat_1=18.4333333333333 +lat_2=18.0333333333333 +x_0=200000 +y_0=200000 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs"
# project:
# proj4string(Output_Shapefile) <- prj
st_crs(Output_Shapefile) <- prj
#> Error in UseMethod("st_crs<-"): no applicable method for 'st_crs<-' applied to an object of class "c('SpatialPolygonsDataFrame', 'SpatialPolygons', 'Spatial', 'SpatialVector')"
And here the solution:
## Solution
# Object with no sp
Output_Shapefile
#> class : SpatialPolygonsDataFrame
#> features : 400
#> extent : 0, 20, 0, 20 (xmin, xmax, ymin, ymax)
#> crs : NA
#> variables : 1
#> names : layer
#> min values : 1
#> max values : 400
# Instead do
Output_Shapefile_sf <- st_as_sf(Output_Shapefile)
Output_Shapefile_sf
#> Simple feature collection with 400 features and 1 field
#> Geometry type: POLYGON
#> Dimension: XY
#> Bounding box: xmin: 0 ymin: 0 xmax: 20 ymax: 20
#> CRS: NA
#> First 10 features:
#> layer geometry
#> 1 1 POLYGON ((0 20, 1 20, 1 19,...
#> 2 2 POLYGON ((1 20, 2 20, 2 19,...
#> 3 3 POLYGON ((2 20, 3 20, 3 19,...
#> 4 4 POLYGON ((3 20, 4 20, 4 19,...
#> 5 5 POLYGON ((4 20, 5 20, 5 19,...
#> 6 6 POLYGON ((5 20, 6 20, 6 19,...
#> 7 7 POLYGON ((6 20, 7 20, 7 19,...
#> 8 8 POLYGON ((7 20, 8 20, 8 19,...
#> 9 9 POLYGON ((8 20, 9 20, 9 19,...
#> 10 10 POLYGON ((9 20, 10 20, 10 1...
st_crs(Output_Shapefile_sf) <- prj
Output_Shapefile_sf
#> Simple feature collection with 400 features and 1 field
#> Geometry type: POLYGON
#> Dimension: XY
#> Bounding box: xmin: 0 ymin: 0 xmax: 20 ymax: 20
#> Projected CRS: +proj=eqdc +lat_0=17.8333333333333 +lon_0=-66.4333333333333 +lat_1=18.4333333333333 +lat_2=18.0333333333333 +x_0=200000 +y_0=200000 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs
#> First 10 features:
#> layer geometry
#> 1 1 POLYGON ((0 20, 1 20, 1 19,...
#> 2 2 POLYGON ((1 20, 2 20, 2 19,...
#> 3 3 POLYGON ((2 20, 3 20, 3 19,...
#> 4 4 POLYGON ((3 20, 4 20, 4 19,...
#> 5 5 POLYGON ((4 20, 5 20, 5 19,...
#> 6 6 POLYGON ((5 20, 6 20, 6 19,...
#> 7 7 POLYGON ((6 20, 7 20, 7 19,...
#> 8 8 POLYGON ((7 20, 8 20, 8 19,...
#> 9 9 POLYGON ((8 20, 9 20, 9 19,...
#> 10 10 POLYGON ((9 20, 10 20, 10 1...
# Back to sp
Output_Shapefile <- as(Output_Shapefile_sf, "Spatial")
Output_Shapefile
#> class : SpatialPolygonsDataFrame
#> features : 400
#> extent : 0, 20, 0, 20 (xmin, xmax, ymin, ymax)
#> crs : +proj=eqdc +lat_0=17.8333333333333 +lon_0=-66.4333333333333 +lat_1=18.4333333333333 +lat_2=18.0333333333333 +x_0=200000 +y_0=200000 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs
#> variables : 1
#> names : layer
#> min values : 1
#> max values : 400
Created on 2025-03-30 with reprex v2.1.1