Sine Regression in R

Hi everyone,

I am trying to fit a sine function on one year of wind data. I have  
two
questions below.

Looking around on the net I managed to get the following:

Sine Equation: y = a + b * sin( c + d*x )

b is the amplitude, c is the phase shift, d is something deal with
periodicty of data*.*

This can be linearised by   sin( c+dx ) = cos(c) * sin(dx) + sin(c) *
cos(dx).

If one calls dx = x1

y = a + b * sin( c + d*x )
y = a + b * [cos(c) * sin(x1) + sin(c) * cos(x1)]
y = a +  b * cos(c) * sin(x1) + b * sin(c) * cos(x1)
y = a +  b1 * sin(x1) + b2 * cos(x1)

where b1 = b * cos(c) and  b2 =  b * sin(c)

This works fine for me as I am not interested in the value for b and  
c. By
trial and error I also detemined that the sensibel value for d is  
1/58. I
have 366 days of data and want to fit a single sine onto it.

*First question*: 1/ 58 = (2 pi) / 366. I guess 366 is the period of  
my
data, I have 366 days. so *d = (2 pi) / Period*. Is this correct.
*Second question*: I reckon that all of this looks very DIY. Is  
there a
better way to do this in R? Maybe through a package I dont know?

Thanks in advance

Paolo