.02

No problem, here's the subroutine which creates the circles.

What happens is a gap once a circle gets big enough. Happens in all bigger rings and part is reflected, suggesting a sign error.

This is the same routine the other ringmaps use which really puzzles me. The only difference is that this routine does not convert to a map projection since I'm plotting lat-lon directly.

SUB create_circle (rlat,rlon,radius)
    LOCAL i
    !  
    ! ----------------------------------------------------
    ! COMPUTE A CIRCLE OF RADIUS radius (km) AT CENTER rlat, rlon
    LET radlat = rlat*dtr         ! CENTER LAT IN RADIANS
    LET radlon = rlon*dtr         ! CENTER LON IN RADIANS
    LET radterra = 6371.0         ! RADIUS OF THE EARTH (km)
    LET theta = radius/radterra
    LET st = sin(theta)
    LET ct = cos(theta)
    FOR i= 0 to 360
        LET angl = i*dtr
        LET sl = sin(radlon)
        LET cl = cos(radlon)
        LET cp = cos(radlat)
        LET sp = sin(radlat)
        LET x = st*cos(angl)
        LET y = st*sin(angl)
        LET xp =  x*sp + ct*cp
        LET zp = -x*cp + ct*sp
        LET cpf = (1. - zp*zp)^0.5
        LET vlat = asin(zp)*rtd   ! LATITUDE
        LET sinang = y/cpf
        LET ang = asin(sinang)
        ! DETERMINE QUADRANTS
        ! FIRST OR THIRD QUADRANT
        IF xp < 0 then
           IF y < 0. then LET ang = abs(ang) + pi
           IF y >= 0. then LET ang = pi - ang
        END IF
        !
        LET ang = ang + radlon
        IF ang > 2.*pi then LET ang = ang - 2.*pi
        LET ulon = ang*rtd        ! LONGITUDE
        IF ulon > 180.0 then LET ulon = ulon - 360.0
        LET cords(i,1) = ulon
        LET cords(i,2) = vlat
    NEXT i
END SUB
!

Roger