A NXYZ file is an ASCII text file. The first line is an integer with the number of coordinates N, followed by N lines with 3 decimal numbers representing the cartesian coordinates x, y, z of each point. Multiple frames can be concatenated.
0.54 2.24 -1.12
0.59 2.63 -1.03
0.56 2.78 -0.92
0.51 2.68 -0.79
For closed rings, the first and last points should have the same coordinates.