curvature versus slope
  n = 3082775 
  X=0, Y = 43.70 +/- 20.22 
  Weighted least-squares fit:  Y = 56.3 + 1.924 X  + -0.02061 X**2 

slope versus dZ, curvature < 5
  n = 473539 

  Weighted least-squares fit:  Y = 70.5 + -0.019 X  + 0.00179 X**2 
     at X = 100, Y = 86.4 
     effective RMSE xy = 78.6 

slope versus dZ, curvature < 15
  n = 1127652 

  Weighted least-squares fit:  Y = 70.5 + -0.022 X  + 0.00202 X**2 

curvature versus dZ, slope < 10
  n = 17160 
  X=0, Y = 73.89 +/- 42.47 
  Weighted least-squares fit:  Y = 70.2 + 1.991 X  + -0.04392 X**2 


Number of samples 3115562
Max dz = 600
Mean dz = 75
RMS dz = 92.822411087
100cm = 71.2509011215 percentile value of dz