Labeling two contours with direct.labels

I'm trying to compare two scalar fields and want to draw them in the same plot using contours labeling their values with directlabels. The thing is, I'm not able to use two direct labels in the same plot.

Example:

library(ggplot2)
library(data.table)
library(directlabels)
grid <- expand.grid(lon = seq(0, 360, by = 2), lat = seq(-90, 0, by = 2))
grid$z <- with(grid, cos(lat*pi/180))
grid$z2 <- with(grid, sin(lat*pi/180))
grid.long <- melt(grid, id.vars = c("lon", "lat"))

# Manually adding two geom_dl's
ggplot(grid, aes(lon, lat)) +
  geom_contour(aes(z = z), color = "black") +
  geom_contour(aes(z = z2), color = "red") +
  geom_dl(aes(z = z2, label = ..level..), stat = "contour", method = "top.pieces", color = "red") +
  geom_dl(aes(z = z, label = ..level..), stat = "contour", method = "top.pieces", color = "black")

Only one variable is labeled.

Another way:

ggplot(grid.long, aes(lon, lat)) +
  geom_contour(aes(z = value, color = variable)) +
  geom_dl(aes(z = value, label = ..level.., color = variable), 
          stat = "contour", method = "top.pieces")

Any solution?

Thanks!

One solution is to provide different method= argument for the second geom_dl() call.

ggplot(grid, aes(lon, lat)) +
      geom_contour(aes(z = z), color = "black") +
      geom_contour(aes(z = z2), color = "red") +
      geom_dl(aes(z = z2, label = ..level..), stat = "contour", method = "top.pieces", color = "red") +
      geom_dl(aes(z = z, label = ..level..), stat = "contour", method = "bottom.pieces", color = "black")