[R] package "sgeostat"

[Yan Yu]

Greetings, all:
  I am wondering have anyone used package "sgeosta" before,
I have a Q about its variogram fitting function:
fit.exponential, fit.gaussian and fit.wave

they ask for a few parameters, which I have no clue how to set them..
e.g., they list this example:
maas.vmod<-fit.gaussian(maas.v,c0=60000,cg=110000,ag=800,plot.it=TRUE,
iterations=30

In the manual page, they list the meaning of those paramters that have
model dependent meanings:

c0:                        initial estimate for nugget effect, valid for all
variogram types, partial sill (cX) and
                        (asymptotical) range (aX) as follows:
 ce, ae
                        initial estimates for the exponential variogram
model
 cg, ag
                        initial estimates for the gaussian variogram model
 cs, as
                        initial estimates for the sperical variogram model
 cw, aw
                        initial estimates for the periodical variogram model

Sorry for my ignorance on those models, my Qs is:
1) what is the rule of thumb to set the above parameters?
2) Does it really matter how I set those initial estimates? How much
influence the initial parameter setting is going to have on the final
model fitting?
3) How do I know if I set those parameters right or way off?

thanks a lot!
yan