A point set is a collection of points usually stored as a sequence of coordinates.

Point sets are non-structured data, easy to visualize, more and more commonly avalaible via 3D scanners.

1.Colored point set

To each point, a color information or a normal vector can be also attached.

Here is an example of a Mandelbrot set, where each pixel point is colored according to the number of iterations

which stay in the disc , starting from .

Here is another example of the Newton iteration set, where each pixel point is colored according to which root of , the Newton iteration

converges to, starting from .

2.Axel file format

The file format used in axel to store point sets is the following.

<pointset name="walnut" size="nbpts" color="rgb">
x0 y0 z0 nr0 ng0 nb0 
x1 y1 z1 nr1 ng1 nb1
...
</pointset>

The size nbpts is the number of points which are stored. The blue parts are optional; nri ngi nbi are integers between 0 and 255 describing the color.