curvature versus slope
  n = 4542507 
  X=0, Y = 18.24 +/- 13.74 
  Weighted least-squares fit:  Y = 9.9 + 1.578 X  + -0.00873 X**2 

slope versus dZ, curvature < 5
  n = 56006 

  Weighted least-squares fit:  Y = 3.1 + 0.107 X  + 0.00060 X**2 
     at X = 100, Y = 19.8 
     effective RMSE xy = 30.7 

slope versus dZ, curvature < 15
  n = 314559 
  X=0, Y = 1.95 +/- 0.85 
  Weighted least-squares fit:  Y = 3.7 + 0.069 X  + 0.00117 X**2 

curvature versus dZ, slope < 10
  n = 1657724 
  X=0, Y = 3.75 +/- 2.44 
  Weighted least-squares fit:  Y = 4.2 + 0.105 X  + 0.00139 X**2 


Number of samples 4548832
Max dz = 900
Mean dz = 8
RMS dz = 17.6635217327
100cm = 99.8470596408 percentile value of dz
Mean dz (curv<=5) = 3
RMS dz (curv<=5) = 7.48331477355