I have built a model from cryo-em density map, now I am going to create a model of a filament (have a length of the pitch, over 1000 A) from it.

I think the command 'sym' can do it, but not easy for me. I have tried many times.

sym  #0  group  h,rise,twist,100

or 

sym  #0  group  c2*h,rise,twist,100 coord #1

or

sym  #0  group  h,2.292,179.6,100 coord #1

the model is wrong

I also try to measure the symmetry first 

and 

sym  #0  group #1

it is almost right, but I need much longer, how set it? using the 'n' parameter? and how?

and if I want to set rise and twist myself, how to do it?

Best wishes, 

Yaowang