title: Plot 3d scattered data using gnuplot
body: <p>Hi I just got some 3d scattered data (the data name is just <code>data.txt</code>) which look like the following:</p>
  
  <pre><code>0 0 0 
  -1.08051e-16 -1.73991e-16 -1.79157e-16 
  -1.02169e-15 -1.19283e-15 5.92632e-16 
  3.41114e-16 -1.02211e-15 3.19436e-15 
  -4.51742e-15 -5.18861e-15 -4.60754e-15 
  -2.00685e-15 -4.67813e-15 -4.86101e-15 
  -9.82727e-16 -2.24413e-15 -5.87927e-16 
  -7.74439e-16 -9.73515e-16 -1.69707e-15 
  4.32668e-16 2.15869e-15 -2.25004e-15 
  -3.74495e-15 -2.20596e-15 -7.33201e-16 
  -4.97941e-16 -5.45749e-16 -2.93136e-15 
  -2.40174e-15 -4.31022e-15 7.13531e-15 
  -4.58812e-15 -4.38568e-15 -9.99635e-16 
  -7.00716e-15 7.53852e-15 -8.484e-15 
  4.50028e-15 2.2255e-15 2.32808e-15 
  -8.57887e-15 3.09127e-15 -3.49207e-15 
  -2.0608e-16 -6.06078e-15 -6.07822e-16 
  -7.76829e-15 -1.47001e-14 -1.08924e-14 
  1.04016e-15 6.33122e-16 -2.11985e-15 
  2.33557e-15 -7.92667e-15 2.52748e-15 
  6.94335e-15 3.70286e-15 -1.44815e-15
  .........
  </code></pre>
  
  <p>the 1st,2nd and 3rd column represent x,y and z axis, respectively.
  I'd like to use splot command to plot these data. Can anyone kindly give some suggestions? Thanks.</p>