R help - Jun 2004 - Is there a function for Principal Surface?

Dear All
 
I know there are functions (PCURVE, PRINCURVE) in R packages to estimate
the principal curve given a set of data.
 
Now, I am wondering if there are some functions for estimating the 
Principal Surface?
 
Please give me a hint if you know some function or software (not limited
to R) to be used for Principal Surface.
 
Thanks for your help.
 
Fred
 

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