test <- data.frame(
  deg = c(  0.0,   16.87,  16.88,  33.75,  50.62,  50.63,  67.5,   84.37,
           84.38, 101.25, 118.12, 118.13, 135.0,  151.87, 151.88, 168.75,
          185.62, 185.63, 202.5,  219.37, 219.38, 236.25, 253.12, 253.13,
          270.0,  286.87, 286.88, 303.75, 320.62, 320.63, 337.5,  354.37,
          354.38)
)

test$heading <- heading(test$deg)
test