R help - Aug 2013 - Plotting GAM fit using RGL

Hello all,

I?ve fitted a bivariate smoothing model (with GAM) to some data, using two
explanatory variables, x and y.  Now I?d like to add the surface corresponding
to my fit to a 3D scatterplot generated using plot3d().

My approach so far is to create a grid of x and y values and the corresponding
predicted values and to try to use surface3d with that grid.

grid <- expand.grid(x = seq(-1,1,length=20),
                    y = seq(-1,1, length=20))

grid$z <- predict(fit.nonparametric, newdata=grid)

surface3d(grid$x, grid$y, matrix(grid$z, nrow=length(grid$x),
ncol=length(grid$y)))

This however plots a number of surfaces that do not look like the fitted surface
obtained by vis.gam(fit.nonparametric which actually looks a lot like the
?truth? (I?m using simulated data so I know the true regression surface).

I think I?m using surface3d wrong but I can?t seem to spot my mistake. 

Thanks!

On Aug 15, 2013, at 2:23 AM, Lucas Holland wrote:
> Hello all,
> 
> I?ve fitted a bivariate smoothing model (with GAM) to some data, using two
explanatory variables, x and y.  Now I?d like to add the surface corresponding
to my fit to a 3D scatterplot generated using plot3d().
> 
> My approach so far is to create a grid of x and y values and the
corresponding predicted values and to try to use surface3d with that grid.
> 
> grid <- expand.grid(x = seq(-1,1,length=20),
>                    y = seq(-1,1, length=20))
> 
> grid$z <- predict(fit.nonparametric, newdata=grid)
> 
> surface3d(grid$x, grid$y, matrix(grid$z, nrow=length(grid$x),
ncol=length(grid$y)))
> 
?surface3d
# Should be:

 surface3d( unique(grid$x), unique(grid$y),
                    z= matrix(grid$z, nrow=length(grid$x), ncol=length(grid$y)))

> This however plots a number of surfaces that do not look like the fitted
surface obtained by vis.gam(fit.nonparametric which actually looks a lot like
the ?truth? (I?m using simulated data so I know the true regression surface).
> 
> I think I?m using surface3d wrong but I can?t seem to spot my mistake. 

Always look at the Arguments section of help pages carefully.

-- 
David Winsemius
Alameda, CA, USA