I am using 'amt' package in RStudio, trying to assess habitat selection of a species in an area with telemetry data. My two preliminary problems are:

1. When I import the land data rasters (elevation and land cover) I get this warning message:

Warning message:
In showSRID(uprojargs, format = "PROJ", multiline = "NO", prefer_proj = prefer_proj) :
  Discarded datum Unknown based on GRS80 ellipsoid in Proj4 definition

Is this something to worry about? Since all the individuals' shapefiles and the land data files are in epsg:2100 (Greek Grid) already before importing them in RStudio? I also tried importing them in epsg:4326 (WGS84) but I get the same warning, and also transforming them with transform_coords() function but again get the same warning. Moreover, I tried using the proj4 for the projection that I use, but I still get the same warning.

landcover = projectRaster(landcover, crs="+proj=tmerc +lat_0=0 +lon_0=24 +k=0.9996 +x_0=500000 +y_0=0 +ellps=GRS80 +towgs84=-199.87,74.79,246.62,0,0,0,0 +units=m +no_defs")

#or

landcover = crs("+proj=tmerc +lat_0=0 +lon_0=24 +k=0.9996 +x_0=500000 +y_0=0 +ellps=GRS80 +towgs84=-199.87,74.79,246.62,0,0,0,0 +units=m +no_defs")

2. When I try to extract covariates from the raster files, I get this error, which I have not figured out how to fix.

Error in UseMethod("extract_covariates", x) : 
  no applicable method for 'extract_covariates' applied to an object of class
 "c('RasterStack', 'Raster', 'RasterStackBrick', 'BasicRaster')"

I have already checked the .tif files in ArcMap and they have identical dimensions, and the pixels have values (elevation and land cover of each pixel).

Any suggestions? Thank you in advance.

Code:

library(amt)
library(raster)
library(tidyverse)
library(lubridate)
library(sf)

#Import the land_cover and elevation rasters
landcover = raster("landcover.tif")

#Warning message:
#In showSRID(uprojargs, format = "PROJ", multiline = "NO", prefer_proj = prefer_proj) :
#  Discarded datum Unknown based on GRS80 ellipsoid in Proj4 definition

elevation = raster("elevation.tif")

#Warning message:
#In showSRID(uprojargs, format = "PROJ", multiline = "NO", prefer_proj = prefer_proj) :
#  Discarded datum Unknown based on GRS80 ellipsoid in Proj4 definition

map <- stack(landcover, elevation) 
plot(map) #I can plot and see the maps
extract_covariates(map, where = "both") #Also tried to extract covariates without using stack()

#Error in UseMethod("extract_covariates", x) : 
#  no applicable method for 'extract_covariates' applied to an object of class
# "c('RasterStack', 'Raster', 'RasterStackBrick', 'BasicRaster')"

I am using 'amt' package in RStudio, trying to assess habitat selection of a species in an area with telemetry data. My two preliminary problems are:

1. When I import the land data rasters (elevation and land cover) I get this warning message:

Warning message:
In showSRID(uprojargs, format = "PROJ", multiline = "NO", prefer_proj = prefer_proj) :
  Discarded datum Unknown based on GRS80 ellipsoid in Proj4 definition

Is this something to worry about? Since all the individuals' shapefiles and the land data files are in epsg:2100 (Greek Grid) already before importing them in RStudio? I also tried importing them in epsg:4326 (WGS84) but I get the same warning, and also transforming them with transform_coords() function but again get the same warning. Moreover, I tried using the proj4 for the projection that I use, but I still get the same warning.

landcover = projectRaster(landcover, crs="+proj=tmerc +lat_0=0 +lon_0=24 +k=0.9996 +x_0=500000 +y_0=0 +ellps=GRS80 +towgs84=-199.87,74.79,246.62,0,0,0,0 +units=m +no_defs")

#or

landcover = crs("+proj=tmerc +lat_0=0 +lon_0=24 +k=0.9996 +x_0=500000 +y_0=0 +ellps=GRS80 +towgs84=-199.87,74.79,246.62,0,0,0,0 +units=m +no_defs")

2. When I try to extract covariates from the raster files, I get this error, which I have not figured out how to fix.

Error in UseMethod("extract_covariates", x) : 
  no applicable method for 'extract_covariates' applied to an object of class
 "c('RasterStack', 'Raster', 'RasterStackBrick', 'BasicRaster')"

I have already checked the .tif files in ArcMap and they have identical dimensions, and the pixels have values (elevation and land cover of each pixel).

Any suggestions?

Code:

library(amt)
library(raster)
library(tidyverse)
library(lubridate)
library(sf)

#Import the land_cover and elevation rasters
landcover = raster("landcover.tif")

#Warning message:
#In showSRID(uprojargs, format = "PROJ", multiline = "NO", prefer_proj = prefer_proj) :
#  Discarded datum Unknown based on GRS80 ellipsoid in Proj4 definition

elevation = raster("elevation.tif")

#Warning message:
#In showSRID(uprojargs, format = "PROJ", multiline = "NO", prefer_proj = prefer_proj) :
#  Discarded datum Unknown based on GRS80 ellipsoid in Proj4 definition

map <- stack(landcover, elevation) 
plot(map) #I can plot and see the maps
extract_covariates(map, where = "both") #Also tried to extract covariates without using stack()

#Error in UseMethod("extract_covariates", x) : 
#  no applicable method for 'extract_covariates' applied to an object of class
# "c('RasterStack', 'Raster', 'RasterStackBrick', 'BasicRaster')"