curvature versus slope
  n = 458589 
  X=0, Y = 12.01 +/- 7.58 
  Weighted least-squares fit:  Y = 7.1 + 1.073 X  + -0.00201 X**2 

slope versus dZ, curvature < 5
  n = 7430 

  Weighted least-squares fit:  Y = 4.0 + -0.020 X  + 0.00325 X**2 
     at X = 100, Y = 34.5 
     effective RMSE xy = 53.8 

slope versus dZ, curvature < 15
  n = 38741 

  Weighted least-squares fit:  Y = 3.4 + 0.124 X  + 0.00022 X**2 

curvature versus dZ, slope < 10
  n = 212190 
  X=0, Y = 3.69 +/- 2.07 
  Weighted least-squares fit:  Y = 3.4 + 0.251 X  + -0.00183 X**2 


Number of samples 458871
Max dz = 600
Mean dz = 7
RMS dz = 12.3288280059
100cm = 99.9245975448 percentile value of dz
Mean dz (curv<=5) = 3
RMS dz (curv<=5) = 4.472135955