curvature versus slope
  n = 1118005 
  X=0, Y = 5.74 +/- 2.75 
  Weighted least-squares fit:  Y = 5.2 + 0.335 X  + -0.00202 X**2 

slope versus dZ, curvature < 5
  n = 229221 
  X=0, Y = 5.43 +/- 3.31 
  Weighted least-squares fit:  Y = 5.6 + 0.068 X  + 0.00386 X**2 
     at X = 100, Y = 51.0 
     effective RMSE xy = 79.5 

slope versus dZ, curvature < 15
  n = 554531 
  X=0, Y = 5.78 +/- 3.48 
  Weighted least-squares fit:  Y = 5.9 + 0.016 X  + 0.00574 X**2 

curvature versus dZ, slope < 10
  n = 1024205 
  X=0, Y = 5.99 +/- 3.85 
  Weighted least-squares fit:  Y = 5.8 + 0.152 X  + 0.00244 X**2 


Number of samples 1118008
Max dz = 51
Mean dz = 5
RMS dz = 6.78232998313
100cm = 0 percentile value of dz
Mean dz (curv<=5) = 4
RMS dz (curv<=5) = 6.0