R when I reproject coastscoarse to Robinson using spTransform I get an unwanted horizontal extra line

Question

When I run this code

library(rworldmap)
data("coastsCoarse")
plot(coastsCoarse)
RobinsonProj <-  "+proj=robin +lon_0=0 +x_0=0 +y_0=0 +ellps=WGS84 +datum=WGS84 +units=m +no_defs"
crsLoc <- CRS(RobinsonProj)
coastsCoarse <- sp::spTransform(coastsCoarse, crsLoc)
plot(coastsCoarse)

coastsCoarse is a SpatialLinesDataFrame. I get one plot that looks like the coasts of the continents. The second plot, after projecting into Robinson returns a horizontal line across the top of the plot of the continents. How do I get rid of that line in the projected version? Extra credit for an explanation of how to get rid of Antarctica.

Answer 1

A kind of a workaround that seems to work for this data set (there's no general solution possible with this toolkit)

 x <- sp::spTransform(raster::crop(coastsCoarse, raster::extent(-179.95, 179.95, -90, 90)), crsLoc)
 

That just erases a little from each side of the input data, to avoid the ambiguity of -180/180 longitude way under the hood. (I name the result x to differentiate it from the data in the package).

To get rid of Antarctica 😱 set ymin to -60.