curvature versus slope
  n = 1300202 
  X=0, Y = 40.76 +/- 37.03 
  Weighted least-squares fit:  Y = 65.6 + 0.614 X  + -0.00536 X**2 

slope versus dZ, curvature < 5
  n = 6336 

  Weighted least-squares fit:  Y = 6.0 + 0.106 X  + 0.00037 X**2 
     at X = 100, Y = 20.3 
     effective RMSE xy = 30.5 

slope versus dZ, curvature < 15
  n = 25206 
  X=0, Y = 4.09 +/- 3.03 
  Weighted least-squares fit:  Y = 6.0 + 0.116 X  + 0.00033 X**2 

curvature versus dZ, slope < 10
  n = 27443 
  X=0, Y = 6.50 +/- 3.99 
  Weighted least-squares fit:  Y = 6.7 + -0.012 X  + 0.00273 X**2 


Number of samples 1302500
Max dz = 900
Mean dz = 17
RMS dz = 23.8956062907
100cm = 99.7824952015 percentile value of dz
Mean dz (curv<=5) = 9
RMS dz (curv<=5) = 12.3693168769