A sufficient depth sampling is the prerequisite of accurate ray geometry and travel time computations. But what is "sufficient"? This section demonstrates some effects of insufficient sampling to guide the user: Ray paths suffer most when coming close to the planetary center, which is at infinite depth in the Flat Earth Domain. Artifact travel time triplications emerge if the sampling exaggerates velocity gradients, especially if the sampling produces sharp kinks in the velocity profile.
Diagnostic properties of poor depth sampling are shown in ray path plots, travel time curves and covered epicentral distance as function of take off angle.
What "good sampling" or "bad sampling" means depends on what you wish to compute, and for what purpose. You should always keep this in mind, especially since a very fine sampling consumes very much CPU time in the evaluation.
As in the section on software evaluation, an asymptotic process of comparison can be used to assess the precision of results: if a decrease of depth sample distance does not change the results significantly (with respect to your purpose), then a finer sampling is not necessary.
The relevant results can be obtained using one of the following routines (see the routine tasks section for a more detailed description, as well as the help lines of the individual routines):