curvature versus slope
  n = 502204 
  X=0, Y = 40.64 +/- 17.90 
  Weighted least-squares fit:  Y = 45.2 + 2.461 X  + -0.02663 X**2 

slope versus dZ, curvature < 5
  n = 272879 

  Weighted least-squares fit:  Y = 8.8 + 0.957 X  + -0.00243 X**2 
     at X = 100, Y = 80.3 
     effective RMSE xy = 125.3 

slope versus dZ, curvature < 15
  n = 392812 

  Weighted least-squares fit:  Y = 7.6 + 1.072 X  + -0.00347 X**2 

curvature versus dZ, slope < 10
  n = 11511 
  X=0, Y = 19.61 +/- 8.99 
  Weighted least-squares fit:  Y = 18.9 + 0.872 X  + 0.07012 X**2 


Number of samples 505848
Max dz = 900
Mean dz = 44
RMS dz = 63.9296488337
100cm = 94.5013126473 percentile value of dz