curvature versus slope
  n = 2173919 
  X=0, Y = 15.79 +/- 9.20 
  Weighted least-squares fit:  Y = 39.5 + 3.176 X  + -0.03561 X**2 

slope versus dZ, curvature < 5
  n = 173038 

  Weighted least-squares fit:  Y = 16.5 + 0.488 X  + -0.00391 X**2 
     at X = 100, Y = 26.3 
     effective RMSE xy = 32.1 

slope versus dZ, curvature < 15
  n = 360410 

  Weighted least-squares fit:  Y = 19.9 + 0.238 X  + 0.00084 X**2 

curvature versus dZ, slope < 10
  n = 92573 
  X=0, Y = 14.55 +/- 12.38 
  Weighted least-squares fit:  Y = 15.2 + 6.302 X  + -0.75909 X**2 


Number of samples 2181862
Max dz = 700
Mean dz = 47
RMS dz = 67.2011904656
100cm = 88.2288155713 percentile value of dz