curvature versus slope
  n = 5335916 
  X=0, Y = 8.59 +/- 5.22 
  Weighted least-squares fit:  Y = 11.6 + 5.346 X  + -0.06688 X**2 

slope versus dZ, curvature < 5
  n = 2350616 

  Weighted least-squares fit:  Y = 9.9 + 0.371 X  + -0.00162 X**2 
     at X = 100, Y = 30.7 
     effective RMSE xy = 45.6 

slope versus dZ, curvature < 15
  n = 3760501 

  Weighted least-squares fit:  Y = 10.6 + 0.431 X  + -0.00128 X**2 

curvature versus dZ, slope < 10
  n = 2537583 
  X=0, Y = 10.27 +/- 6.60 
  Weighted least-squares fit:  Y = 10.3 + 2.646 X  + -0.06650 X**2 


Number of samples 5462307
Max dz = 800
Mean dz = 20
RMS dz = 34.8425027804
100cm = 97.413876591 percentile value of dz