curvature versus slope
  n = 2988327 
  X=0, Y = 17.54 +/- 12.97 
  Weighted least-squares fit:  Y = 10.9 + 1.621 X  + -0.00964 X**2 

slope versus dZ, curvature < 5
  n = 45895 

  Weighted least-squares fit:  Y = 2.6 + 0.137 X  + 0.00066 X**2 
     at X = 100, Y = 22.9 
     effective RMSE xy = 35.8 

slope versus dZ, curvature < 15
  n = 217616 

  Weighted least-squares fit:  Y = 2.8 + 0.103 X  + 0.00134 X**2 

curvature versus dZ, slope < 10
  n = 946526 
  X=0, Y = 3.64 +/- 2.09 
  Weighted least-squares fit:  Y = 3.4 + 0.095 X  + 0.00253 X**2 


Number of samples 2992911
Max dz = 900
Mean dz = 8
RMS dz = 19.7484176581
100cm = 99.8295305139 percentile value of dz
Mean dz (curv<=5) = 3
RMS dz (curv<=5) = 8.24621125124