curvature versus slope
  n = 4219210 
  X=0, Y = 33.37 +/- 26.90 
  Weighted least-squares fit:  Y = 32.2 + 1.797 X  + -0.01517 X**2 

slope versus dZ, curvature < 5
  n = 121137 

  Weighted least-squares fit:  Y = 5.3 + -0.028 X  + 0.00164 X**2 
     at X = 100, Y = 18.9 
     effective RMSE xy = 28.4 

slope versus dZ, curvature < 15
  n = 637652 
  X=0, Y = 5.47 +/- 3.49 
  Weighted least-squares fit:  Y = 5.1 + 0.015 X  + 0.00128 X**2 

curvature versus dZ, slope < 10
  n = 1019359 
  X=0, Y = 5.50 +/- 2.91 
  Weighted least-squares fit:  Y = 4.8 + 0.143 X  + -0.00089 X**2 


Number of samples 4221803
Max dz = 900
Mean dz = 10
RMS dz = 16.0
100cm = 99.9225686277 percentile value of dz
Mean dz (curv<=5) = 5
RMS dz (curv<=5) = 6.63324958071