curvature versus slope
  n = 2322610 
  X=0, Y = 31.85 +/- 21.58 
  Weighted least-squares fit:  Y = 48.4 + 2.268 X  + -0.02284 X**2 

slope versus dZ, curvature < 5
  n = 149820 

  Weighted least-squares fit:  Y = 4.9 + 0.371 X  + -0.00131 X**2 
     at X = 100, Y = 28.9 
     effective RMSE xy = 44.7 

slope versus dZ, curvature < 15
  n = 623227 

  Weighted least-squares fit:  Y = 6.6 + 0.337 X  + -0.00078 X**2 

curvature versus dZ, slope < 10
  n = 31861 
  X=0, Y = 7.01 +/- 4.75 
  Weighted least-squares fit:  Y = 6.3 + 1.893 X  + -0.00461 X**2 


Number of samples 2367710
Max dz = 800
Mean dz = 30
RMS dz = 48.1040538832
100cm = 95.1681582626 percentile value of dz