Since update of sp package i get a warning by calling a sp::CRS definition

Question

Since update of sp package i get a warning i did not get before:

 1: In showSRID(uprojargs, format = "PROJ", multiline = "NO") :
  Discarded ellps unknown in CRS definition: +proj=stere +lat_0=90 +lon_0=10 +k=0.93301270189 +x_0=0 +y_0=0 +R=6370040 +units=km +no_defs
2: In showSRID(uprojargs, format = "PROJ", multiline = "NO") :
  Discarded datum unknown in CRS definition

This is a code i use to define CRS

 sp::CRS(
      "+proj=stere +lat_0=90 +lat_ts=90 +lon_0=10 +k=0.93301270189 +x_0=0 +y_0=0 +a=6370040 +b=6370040 +to_meter=1000 +no_defs"
    )

I try to create a projection and it was working before :) But since update i get this warning. What am i doing wrong? Thank you in advance,

Best regards, Andreas

Answer 1

In your definition, you have parameters a and b --- these refer to the radii of the ellipsoid representation of the earth. As they are the same, you are using a sphere. The new version of the PROJ library require that, if you use the proj4 notation, you must used the WGS84 (or closely related) datum. Otherwise, you need to provide the EPSG code, or WKT notation. So something like this:

p4 <- "+proj=stere +lat_0=90 +lat_ts=90 +lon_0=10 +k=0.93301270189 +units=km +datum=WGS84"
sp::CRS(p4)
#CRS arguments:
# +proj=stere +lat_0=90 +lon_0=10 +k=0.93301270189 +x_0=0 +y_0=0 +units=km  +datum=WGS84 +units=m +no_defs 

Since there does not seem to be a EPSG code for this CRS, you would need to provide WKT description. I found this one

wkt <- 'PROJCS["unknown",
GEOGCS["unknown",
    DATUM["unknown",
        SPHEROID["unknown",6370040,0]],
    PRIMEM["Greenwich",0,
        AUTHORITY["EPSG","8901"]],
    UNIT["degree",0.0174532925199433,
        AUTHORITY["EPSG","9122"]]],
PROJECTION["Polar_Stereographic"],
PARAMETER["latitude_of_origin",90],
PARAMETER["central_meridian",10],
PARAMETER["scale_factor",0.93301270189],
PARAMETER["false_easting",0],
PARAMETER["false_northing",0],
UNIT["kilometre",1000,
    AUTHORITY["EPSG","9036"]],
AXIS["Easting",SOUTH],
AXIS["Northing",SOUTH]]'

But that still does not work because of the datum being unknown 

CRS(SRS_string=wkt)

#CRS arguments:
# +proj=stere +lat_0=90 +lon_0=10 +k=0.93301270189 +x_0=0 +y_0=0 +R=6370040 +units=km +no_defs 
#Warning messages:
#1: In showSRID(SRS_string, format = "PROJ", multiline = "NO") :
#  Discarded ellps unknown in CRS definition: +proj=stere +lat_0=90 +lon_0=10 +k=0.93301270189 +x_0=0 +y_0=0 +R=6370040 +units=km +no_defs
#2: In showSRID(SRS_string, format = "PROJ", multiline = "NO") :
#  Discarded datum unknown in CRS definition