curvature versus slope
  n = 234796 
  X=0, Y = 5.66 +/- 2.62 
  Weighted least-squares fit:  Y = 5.2 + 0.326 X  + -0.00161 X**2 

slope versus dZ, curvature < 5
  n = 46709 
  X=0, Y = 3.00 +/- 1.90 
  Weighted least-squares fit:  Y = 5.9 + 0.078 X  + -0.00006 X**2 
     at X = 100, Y = 13.0 
     effective RMSE xy = 18.3 

slope versus dZ, curvature < 15
  n = 115462 
  X=0, Y = 7.14 +/- 4.40 
  Weighted least-squares fit:  Y = 6.2 + 0.013 X  + 0.00334 X**2 

curvature versus dZ, slope < 10
  n = 214580 
  X=0, Y = 6.30 +/- 3.87 
  Weighted least-squares fit:  Y = 6.1 + 0.106 X  + 0.00384 X**2 


Number of samples 234807
Max dz = 39
Mean dz = 5
RMS dz = 6.8556546004
100cm = 0 percentile value of dz
Mean dz (curv<=5) = 5
RMS dz (curv<=5) = 6.2449979984