[R] interaction term and scatterplot3d

[Patrick Giraudoux]

Dear Listers,

I would be interested in representing a trend surface including an 
interaction term z = f(x,y,x.y) - eg the type of chart obtained with 
persp() or wireframe(), then adding datapoints as a cloud, ideally with 
dots which are under the surface in a color, and those who are above in 
another color. An other option would be to draw segments between the 
dots and the ground of the chart.

scatterplot3d looks like being close to do such things except it does 
not to include (to my knowledge) a coefficient for the interaction term 
(thus just model z = f(x,y).

Does anybody has an idea where to start with this and the main steps? Or 
a place/website where some script examples can be found?

Patrick