curvature versus slope
  n = 910858 
  X=0, Y = 41.49 +/- 24.43 
  Weighted least-squares fit:  Y = 53.6 + 1.950 X  + -0.02147 X**2 

slope versus dZ, curvature < 5
  n = 129003 

  Weighted least-squares fit:  Y = 12.8 + 0.126 X  + 0.00229 X**2 
     at X = 100, Y = 48.3 
     effective RMSE xy = 73.2 

slope versus dZ, curvature < 15
  n = 336771 

  Weighted least-squares fit:  Y = 13.6 + 0.143 X  + 0.00237 X**2 

curvature versus dZ, slope < 10
  n = 20097 
  X=0, Y = 12.29 +/- 7.39 
  Weighted least-squares fit:  Y = 11.0 + 2.178 X  + 0.01727 X**2 


Number of samples 928278
Max dz = 900
Mean dz = 42
RMS dz = 64.3117407633
100cm = 89.6472823874 percentile value of dz