curvature versus slope
  n = 402372 
  X=0, Y = 60.11 +/- 20.76 
  Weighted least-squares fit:  Y = 68.3 + 1.237 X  + -0.01174 X**2 

slope versus dZ, curvature < 5
  n = 100054 

  Weighted least-squares fit:  Y = 0.6 + 1.994 X  + -0.01156 X**2 
     at X = 100, Y = 84.4 
     effective RMSE xy = 132.6 

slope versus dZ, curvature < 15
  n = 190226 

  Weighted least-squares fit:  Y = 4.8 + 2.565 X  + -0.01524 X**2 

curvature versus dZ, slope < 10
  n = 1032 
  X=0, Y = 6.50 +/- 4.43 
  Weighted least-squares fit:  Y = 8.0 + 3.066 X  + 0.14591 X**2 


Number of samples 406119
Max dz = 900
Mean dz = 97
RMS dz = 147.390637423
100cm = 73.7707420731 percentile value of dz