Enhance constrast of edges on procedure texture

[rdb]

You can use show_frustum() to make the frustum appear visually, which may help in tweaking it.
Also see this post, it touches on frustum adjustment methods:

Sample: using directional lights+shadows effectively

Using directional lights with shadowing can often be a stumbling block for Panda users. Fitting the frustum around the scene properly can be tricky. So here is a little sample program that shows how to use directional lights effectively. It includes a function that will tightly fit the frustum around the scene, for static, smaller scenes (press 1 to use it automatically). This is great for smaller scenes or where the light is static and there is no time-of-day, because it is slow to compute …