test_spiral.f90 running
      xmin      xmax      ymin      ymax
      zmin      zmax       atx       aty
 -1.000000  1.000000 -1.000000  1.000000
 -0.984507  2.051590  0.000000 -0.020000

 -2.000000  2.000000 -2.000000  2.000000
 -0.968028  2.997444  0.000000 -0.040000


 -4.000000  4.000000 -4.000000  4.000000
 -0.932118  5.212456  0.000000 -0.080000


  0.000000  1.000000  0.000000  1.000000
  0.000000  1.750000  0.000000  0.000000


 -0.100000  0.100000 -0.100000  0.100000
 -0.998495  1.076034  0.000000 -0.002000