curvature versus slope
  n = 507395 
  X=0, Y = 40.86 +/- 27.51 
  Weighted least-squares fit:  Y = 67.2 + 1.354 X  + -0.01381 X**2 

slope versus dZ, curvature < 5
  n = 20667 

  Weighted least-squares fit:  Y = 10.7 + 0.219 X  + 0.00105 X**2 
     at X = 100, Y = 43.1 
     effective RMSE xy = 65.6 

slope versus dZ, curvature < 15
  n = 50983 

  Weighted least-squares fit:  Y = 10.1 + 0.493 X  + -0.00074 X**2 

curvature versus dZ, slope < 10
  n = 4884 
  X=0, Y = 9.37 +/- 6.31 
  Weighted least-squares fit:  Y = 8.2 + 3.718 X  + -0.27180 X**2 


Number of samples 513660
Max dz = 900
Mean dz = 57
RMS dz = 83.6540495135
100cm = 82.7259276564 percentile value of dz