curvature versus slope
  n = 278361 
  X=0, Y = 45.97 +/- 36.62 
  Weighted least-squares fit:  Y = 70.2 + 0.886 X  + -0.00788 X**2 

slope versus dZ, curvature < 5
  n = 5433 

  Weighted least-squares fit:  Y = 1.4 + 0.834 X  + -0.00121 X**2 
     at X = 100, Y = 72.8 
     effective RMSE xy = 114.3 

slope versus dZ, curvature < 15
  n = 22087 

  Weighted least-squares fit:  Y = 4.8 + 0.854 X  + -0.00156 X**2 

curvature versus dZ, slope < 10
  n = 1893 
  X=0, Y = 4.10 +/- 4.03 
  Weighted least-squares fit:  Y = 4.0 + 4.704 X  + -0.08943 X**2 


Number of samples 281889
Max dz = 900
Mean dz = 73
RMS dz = 116.198106697
100cm = 75.8699346197 percentile value of dz