DIGITIZING CIRCLES?

[ANNE M. SMITH]

We are digitizing field boundaries from an aerial photography.  A centre pivot 
irrigation system had been used on some fields and we need to digitize circles. 
Any suggestions on how to digitize circles?  I did read in an earlier message 
about v.circle.  Can somebody tell me where we could locate a copy of v.circle 
and how to use it? 

Thanks

Anne M. Smith
smitha at abrsle.agr.ca