When I read in a shapefile with readOGR, the following warnings are raised.
Warning messages:
1: In OGRSpatialRef(dsn, layer, morphFromESRI = morphFromESRI, ... : Discarded ellps WGS 84 in CRS definition: +proj=merc +a=6378137 +b=6378137 +lat_ts=0 +lon_0=0 +x_0=0 +y_0=0 +k=1 +units=m +nadgrids=@null +wktext +no_defs
2: In OGRSpatialRef(dsn, layer, morphFromESRI = morphFromESRI, ... : Discarded datum WGS_1984 in CRS definition: +proj=merc +a=6378137 +b=6378137 +lat_ts=0 +lon_0=0 +x_0=0 +y_0=0 +k=1 +units=m +nadgrids=@null +wktext +no_defs
3: In showSRID(wkt2, "PROJ") : Discarded ellps WGS 84 in CRS definition: +proj=merc +a=6378137 +b=6378137 +lat_ts=0 +lon_0=0 +x_0=0 +y_0=0 +k=1 +units=m +nadgrids=@null +wktext +no_defs
4: In showSRID(wkt2, "PROJ") : Discarded datum WGS_1984 in CRS definition
5: In sp::proj4string(obj) : CRS object has comment, which is lost in output
What do they mean, and how to tackle them?
