Generates craters onto a mesh using radial functions.<br />
There must be at least two layers to apply this filter:<br />
<ul>
    <li>the layer that contains the target mesh; we assume that this mesh is sufficiently refined;</li>
    <li>the layer that contains the samples which represent the central points of craters.</li>
</ul>

There are three radial functions available to generate craters, two of which are Gaussian and Multiquadric,
and the third is a variant of multiquadric. Blending functions are also provided to blend
the crater elevation towards the mesh surface.
If you want the preview to work, be sure to select the target mesh layer before launching the
filter. You can select this layer by clicking on it in the layer dialog.
