[STATSGRASS] problem on trend surface calculation

[Pierluigi De Rosa]

Dear all,

I wont to try to define a trend surface, now I'm just tring with meude dataset 
to learn it but I have an error. I do this:

 gs<-gstat(id="zinc.uk",formula=zinc~x+y,location=meuse,degree=2)
then
 pgs=predict.gstat(gs,newdata=meuse.grid) 

but I have this error:
polynomial degree only works when no other predictors are given

It seems everythink  fine but I don't know where I wrong...
Can anyone help me??
Thaks
Pierluigi


-- 

Pierluigi De Rosa

Department of Enviromental & Civil engineering 
Faculty of Engineering 
Perugia (Italy)