# Bound box for parametric 3D plots?

I am trying to plot a parametric surface but only in a certain box in 3D space. Namely, I would like to get JMol to plot this:

```
var('s t')
p = [s^2, s^2+t^2, s^2+s*t+s+t]; q = s^2+t^2+s-t+1
parametric_plot3d((p[0]/q,p[1]/q,p[2]/q),(s,-5,5),(t,-5,5), points=[100,100])
```

but restricted to [0,1]x[0,1]x[0,1] (for example). I see that implicit plots work exactly like that, but the singular part of this surface looks quite ugly: http://imgur.com/5IxilIz.

I would be fine with tachyon too, but I haven't been able to figure out how to rotate the camera (I basically want to cut out a chunk of that surface to see a section).