Longitude/latitude of a single point, in degrees; can be a vector of two numbers, a matrix of 2 columns (first one is longitude, second is latitude) or a SpatialPoints* object
p2
As above
n
The requested number of points on the Great Circle
breakAtDateLine
Logical. Return two matrices if the dateline is crossed?
addStartEnd
Logical. Add p1 and p2 to the result?
sp
Logical. Return a SpatialLines object?
sepNA
Logical. Rather than as a list, return the values as a two column matrix with lines seperated by a row of NA values? (for use in 'plot')