curvature versus slope
  n = 3927455 
  X=0, Y = 21.39 +/- 16.71 
  Weighted least-squares fit:  Y = 57.5 + 1.992 X  + -0.01996 X**2 

slope versus dZ, curvature < 5
  n = 30803 

  Weighted least-squares fit:  Y = 5.8 + 0.568 X  + -0.00454 X**2 
     at X = 100, Y = 17.2 
     effective RMSE xy = 25.5 

slope versus dZ, curvature < 15
  n = 177560 

  Weighted least-squares fit:  Y = 7.0 + 0.567 X  + -0.00239 X**2 

curvature versus dZ, slope < 10
  n = 15345 
  X=0, Y = 9.78 +/- 5.70 
  Weighted least-squares fit:  Y = 9.8 + 0.492 X  + 0.14711 X**2 


Number of samples 3946996
Max dz = 900
Mean dz = 47
RMS dz = 66.7008245826
100cm = 88.0284145208 percentile value of dz