curvature versus slope
  n = 497771 
  X=0, Y = 50.22 +/- 22.06 
  Weighted least-squares fit:  Y = 60.1 + 2.119 X  + -0.02377 X**2 

slope versus dZ, curvature < 5
  n = 220265 

  Weighted least-squares fit:  Y = 20.2 + 0.121 X  + 0.00256 X**2 
     at X = 100, Y = 57.8 
     effective RMSE xy = 85.1 

slope versus dZ, curvature < 15
  n = 378831 

  Weighted least-squares fit:  Y = 20.0 + 0.159 X  + 0.00248 X**2 

curvature versus dZ, slope < 10
  n = 6422 
  X=0, Y = 24.47 +/- 13.47 
  Weighted least-squares fit:  Y = 23.8 + 4.338 X  + -1.24594 X**2 


Number of samples 500556
Max dz = 900
Mean dz = 36
RMS dz = 55.1271258094
100cm = 97.448037782 percentile value of dz