curvature versus slope
  n = 828751 
  X=0, Y = 40.29 +/- 21.42 
  Weighted least-squares fit:  Y = 49.3 + 2.186 X  + -0.02290 X**2 

slope versus dZ, curvature < 5
  n = 149425 

  Weighted least-squares fit:  Y = 40.1 + 0.425 X  + -0.00043 X**2 
     at X = 100, Y = 78.3 
     effective RMSE xy = 105.7 

slope versus dZ, curvature < 15
  n = 386769 

  Weighted least-squares fit:  Y = 40.5 + 0.399 X  + 0.00040 X**2 

curvature versus dZ, slope < 10
  n = 12181 
  X=0, Y = 45.23 +/- 17.18 
  Weighted least-squares fit:  Y = 43.8 + 0.278 X  + 0.04747 X**2 


Number of samples 838117
Max dz = 900
Mean dz = 63
RMS dz = 81.5352684426
100cm = 85.638282006 percentile value of dz