src/sankeyCircular.js
function linkAngle (link) {
    var adjacent = Math.abs(link.y1 - link.y0)
    var opposite = Math.abs(link.target.x0 - link.source.x1)

    return Math.atan(opposite / adjacent)
  }
function linkAngle (link) {
    var adjacent = Math.abs(link.y1 - link.y0)
    var opposite = Math.abs(link.target.x0 - link.source.x1)

    return Math.atan(opposite / adjacent)
  }
Return the angle between a straight line between the source and target of the link, and the vertical plane of the node