[R] Help for 3D Plotting Data on 'Irregular' Grid

[Lorenzo Isella]

Dear All,
Here is what I am trying to achieve: I would like to plot some data in 3D.
Usually, one has a matrix of the kind

y_1(x_1) , y_1(x_2).....y_1(x_i)
y_2(x_1) , y_2(x_2).....y_2(x_i)
...........................................
y_n(x_1) , y_n(x_2)......y_n(x_i)


where e.g. y_2(x_1) is the value of y at time 2 at point x_1 (see that 
the grid in x is the same for the y values at all times).
Instead, in my case, the quantity y is observed at each time on a 
different grid in x; in other words not only do I have a different 
number of observations (y values) at each time, but I also have 
observations taken on a a different x grid each time.
As a matter of fact, it is as if I had a set of independent 
observations, for each of which I can create effortlessly a 2D plot, 
that I want to stitch together into a 3D plot.
I have no idea of how to achieve that. Examples I have found with 
lattice or scatterplot3D all assume a regular grid like the one I 
described above.
Any help is really appreciated.
Many thanks

Lorenzo