curvature versus slope
  n = 19211134 
  X=0, Y = 29.73 +/- 20.20 
  Weighted least-squares fit:  Y = 67.7 + 1.676 X  + -0.01699 X**2 

slope versus dZ, curvature < 5
  n = 113585 

  Weighted least-squares fit:  Y = 11.9 + 0.280 X  + -0.00077 X**2 
     at X = 100, Y = 32.2 
     effective RMSE xy = 47.0 

slope versus dZ, curvature < 15
  n = 2013937 

  Weighted least-squares fit:  Y = 10.8 + 0.344 X  + -0.00046 X**2 

curvature versus dZ, slope < 10
  n = 22537 
  X=0, Y = 16.61 +/- 12.10 
  Weighted least-squares fit:  Y = 17.6 + -1.460 X  + 0.35786 X**2 


Number of samples 19431495
Max dz = 800
Mean dz = 34
RMS dz = 47.2016948848
100cm = 95.4593663534 percentile value of dz