Adding points to a wireframe: 'x and units must have length >0' error

Hi,

I'm trying to follow the suggestions given by Deepayan Sarkar in this
message:

http://tolstoy.newcastle.edu.au/R/help/05/11/16135.html

to plot 3-D points on a wireframe plot. The problem is that I keep  
getting a
partly formed plot- with the colored lattice visible but no axis  
labels or
additional points- with the error message "error using packet 1, 'x'  
and
'units' must have length >0".  Does anyone know what I'm doing  
wrong? The
code I've been using is:

# generate some fake data
data.frame(x = seq(-4, 0, 0.5), y = seq(0, 40, 5))-> df
expand.grid(x = df$x, y = df$y) -> gridd
(gridd$y* gridd$x) -> gridd$z

data.frame(x = runif(10, -4, 0), y = runif(10, 0, 40))-> pts1
pts1$z <- pts1$x*pts1$y

# plot

wireframe(z ~ y*x, gridd, drape = TRUE, colorkey= TRUE,
         scales = list(arrows = FALSE),
         pts = pts1,
         panel.3d.wireframe =
         function(x, y, z,xlim, ylim, zlim, xlim.scaled, ylim.scaled,
zlim.scaled, pts1, ...)

                   {
             panel.3dwire(x = x, y = y, z = z,
                          xlim = c(-4, 0),
                          ylim = c(0, 40),
                          zlim = c(-160, 0),
                          xlim.scaled = c(-0.5, 0.5),
                          ylim.scaled = c(-0.5, 0.5),
                          zlim.scaled = c(-0.5, 0.5),
                          ...)
       xx <- xlim.scaled[1] + diff(xlim.scaled) * (pts1$x - xlim[1]) /
diff(xlim)
       yy <- ylim.scaled[1] + diff(ylim.scaled) * (pts1$y - ylim[1]) /
diff(ylim)
       zz <- zlim.scaled[1] + diff(zlim.scaled) * (pts1$z - zlim[1]) /
diff(zlim)
             panel.3dscatter(x = xx,

                             y = yy,
                             z = zz,
                             xlim = xlim,
                             ylim = ylim,
                             zlim = zlim,
                             xlim.scaled = xlim.scaled,
                             ylim.scaled = ylim.scaled,
                             zlim.scaled = zlim.scaled,
                             ...)
         })

Thanks so much!

-Megan Bartlett

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