test_spiral.c running 
xmin= -1.000000, xmax=  1.000000, ymin= -1.000000, ymax=  1.000000 
zmin= -0.955168, zmax=  2.051590, atx= -0.009901,  aty= -0.049505 

xmin= -2.000000, xmax=  2.000000, ymin= -2.000000, ymax=  2.000000 
zmin= -0.928182, zmax=  2.997432, atx= -0.019802,  aty= -0.059406 

xmin= -0.010000, xmax= -1.000000, ymin=  0.010000, ymax=  1.000000 
zmin= -0.359440, zmax=  1.100810, atx= -0.696139,  aty=  0.010000 

xmin=  0.010000, xmax=  1.000000, ymin=  0.010000, ymax=  1.000000 
zmin=  0.302981, zmax=  1.749987, atx=  0.068812,  aty=  0.010000 

xmin= -0.010000, xmax= -1.000000, ymin= -0.010000, ymax= -1.000000 
zmin= -0.954951, zmax=  0.926281, atx= -0.010000,  aty= -0.049208