curvature versus slope
  n = 370281 
  X=0, Y = 39.70 +/- 21.05 
  Weighted least-squares fit:  Y = 55.5 + 2.188 X  + -0.02415 X**2 

slope versus dZ, curvature < 5
  n = 51419 

  Weighted least-squares fit:  Y = 22.3 + 0.534 X  + 0.00093 X**2 
     at X = 100, Y = 85.0 
     effective RMSE xy = 128.8 

slope versus dZ, curvature < 15
  n = 127297 

  Weighted least-squares fit:  Y = 23.1 + 0.514 X  + 0.00139 X**2 

curvature versus dZ, slope < 10
  n = 3590 
  X=0, Y = 23.85 +/- 16.89 
  Weighted least-squares fit:  Y = 26.4 + 2.562 X  + -0.03907 X**2 


Number of samples 373481
Max dz = 900
Mean dz = 71
RMS dz = 111.220501707
100cm = 78.5520548569 percentile value of dz