// For each section location, define x,y,z coordinates so it can be
// displayed in 3-D

proc endpt() {
  P=(n3d()-1)*$1

  x_d3($1)=x3d(P)
  y_d3($1)=y3d(P)
  z_d3($1)=z3d(P)

}
proc fracpt() { local posn, A
  A=$1
  posn=$2
  x_d3(posn)=x3d(i-1) + (x3d(i) - x3d(i-1))*A
  y_d3(posn)=y3d(i-1) + (y3d(i) - y3d(i-1))*A
  z_d3(posn)=z3d(i-1) + (z3d(i) - z3d(i-1))*A

}
proc map_segments_to_3d() {

    forall {
    
    insert d3
    i=0
    endpt(0)

    for (x) {if (x > 0 && x < 1) {

      while (arc3d(i)/L < x) {
        i += 1
      }
      D=arc3d(i) - arc3d(i-1)
      if (D <= 0) {
      printf("\t\t * %s had a D < 0\n", secname())
      }
      alpha = (x*L - arc3d(i-1))/D
      fracpt(alpha,x)

    }}
    endpt(1)

  }
}