1.4.2.8 Isosurface not rendering properly?

"My isosurface is not rendering properly: there are holes or random noise or big parts or even the whole isosurface just disappears."

The most common reason for these type of phenomena with isosurfaces is a too low max_gradient value. Use evaluate to make POV-Ray calculate a proper max_gradient for the isosurface (remember to specify a sensible max_gradient even when you use evaluate or else the result may not be correct).

Sometimes a too high accuracy value can also cause problems even when the max_gradient is ok. If playing with the latter does not seem to help, try also lowering the accuracy.

Remember that specifying a max_gradient which is too high for an isosurface, although it gives the correct result, is needlessly slow, so you should always calculate the proper max_gradient for each isosurface you make.

Note that there are certain pathological functions where no max_gradient or accuracy will help. These functions usually have discontinuities or similar "ill-behaving" properties. With those you just have to find a solution which gives the best quality/speed tradeoff. Isosurfaces work best with functions which give smooth surfaces.