curvature versus slope
  n = 336223 
  X=0, Y = 62.14 +/- 25.43 
  Weighted least-squares fit:  Y = 67.1 + 1.370 X  + -0.01436 X**2 

slope versus dZ, curvature < 5
  n = 47083 

  Weighted least-squares fit:  Y = 29.3 + 1.034 X  + -0.00449 X**2 
     at X = 100, Y = 87.7 
     effective RMSE xy = 129.9 

slope versus dZ, curvature < 15
  n = 148124 

  Weighted least-squares fit:  Y = 35.4 + 0.886 X  + -0.00323 X**2 

curvature versus dZ, slope < 10
  n = 1336 
  X=0, Y = 33.33 +/- 11.75 
  Weighted least-squares fit:  Y = 32.1 + 6.777 X  + -0.16629 X**2 


Number of samples 340356
Max dz = 900
Mean dz = 77
RMS dz = 95.0
100cm = 73.5391766268 percentile value of dz
Mean dz (curv<=5) = 66
RMS dz (curv<=5) = 74.4781847255