function self_conjugate,visin,CRIT=crit

; Makes a visibility structure self-conjugate, i.e. the visibilities on the
; lower half of the uv circle are the conjugates of those on the upper half:
;  VIS(-u,-v) = conj(VIS(u,v))
; This is done by averaging neg & pos v's and conjugating
; i.e. vis_cc(u,v)=0.5*(vis(u,v)+vis(-u,-v)) for all u and v
; WARNING: This assumes the u,v values are nearly symmetric

default,crit,1.e-5 ; max u,v asymmetry permitted

neg=where(visin.v lt 0,nneg)
pos=where(visin.v gt 0,npos)
if npos ne nneg then message,'numbers of neg & pos v values are not equal'

; check to see that u & v are symmetric
vmaxdiff=max(abs(visin[pos].v + visin[neg].v))
if vmaxdiff gt crit, then message,'WARNING: v(neg) + v(pos) gt '+strtrim(crit)',/info
umaxdiff=max(abs(visin[pos].u - visin[neg].u))
if umaxdiff gt crit, then message,'WARNING: u(neg) - u(pos) gt '+strtrim(crit)',/info

vis=visin  ; the output version to be modified
; symmetrize the v values
vis[pos].v = 0.5*(visin[pos].v + visin[neg].v)
vis[neg].v = 0.5*(visin[pos].v + visin[neg].v)
; symmetrize the u values
vis[pos].u = 0.5*(visin[pos].v + visin[neg].v)
vis[neg].u = 0.5*(visin[pos].v + visin[neg].v)

; make the visibilities self conjugate
vis(pos).obsvis = 0.5*(visin[pos].obsvis+conj(visin[neg].obsvis))
vis(neg).obsvis = 0.5*(conj(visin[pos].obsvis)+visin[neg].obsvis)

return,vis
end