Expert Pass 1 & 2 Tab
From ZBrush Info
If you're looking at these controls, you're getting deeply into normal maps. Different applications can use normal maps in subtly different ways, and the expert options allow fine-tuning of normal maps to achieve exactly the desired result. It's more likely that these options will be set via configuration files than by hand.
- Figure: Normal mapping expert panels.
The expert options will not be described in detail in this document, but the next few paragraphs give an idea of some of the issues involved.
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Expert Option Passes
First, notice that many of the controls in the first panel also appear in the second, and vice versa. The expert options are actually applied in two passes. The Expert 1 Pass panel defines options applied in the first pass, and Expert 2 Pass defines options applied in the second pass. The duplication of some of the controls allows certain effects to be applied before or after other effects, as a matter of choice.
Surface Normal Interpolation
In the raycasting process the rays projected out from the low-resolution surface are not projected perpendicularly to each polygon in the low-resolution surface. Instead, the ray directions are typically interpolated in some manner, using either surface normals or vertex normals in the low-resolution surface, in order to account for the fact that the polygons are normally intended as an approximation of a smooth surface. Casting rays straight out from each low-resolution polygon would not take into account this implied smoothness.
At the same time, not all polygons or polygon boundaries should be smoothed. Some of them really do represent flat faces or sharp edges. Standard mesh file formats do not have an agreed-upon method for indicating where smoothing should and should not occur, so normal map generation programs often provide options to allow heuristics during the map generation process. For example, you might wish to indicate that polygonal borders sharper than a given angle should be considered as sharp edges, while less sharp borders should be considered as smooth edges.
In addition, polygon groups often indicate sections of a model that have sharper boundaries with respect to adjacent groups, making it desirable to allow different heuristics at group borders than at polygon borders. This may also be true at UV seam borders.
A number of the expert options, such as the various PreSmooth... and PostSmooth... options relate to these issues.
Map Distortion Issues
Given the amount of translation that is being done from one space (such as the xy coordinates of a normal map texture) to another (such as the tangent space coordinates on the surface of a polygon), it would be surprising if angles in one space always translated into equivalent angles in another space. However, the definition in tangent space of the tangent, normal, and binormal vectors is such that they are supposed to be perpendicular to one another. In order to account for these stretching and distortion affects, adjustments to calculated vectors may be necessary during the normal map generation process. Expert options in ZMapper relating to this include the Orthogonalize... and Derive... options. If you play with these options, you'll often find that changing one changes another, because there are interactions between them.
Expert Options Summary
The expert options panel in ZMapper exists to compensate for the fact that other 3D applications will interpret the subtleties of normal maps in different ways. This is likely to be a general cross-application difficulty, until standards for normal maps have been agreed on and published.
This whole section on expert options was intended to help satisfy the curiosity of those who may be wondering about all of these additional controls, and to give some indication to those who may need to use expert options as to what the options relate to.
Few people should need to actually get this far into normal mapping details, however. ZMapper comes with a large number of configuration files (see section #Configuration and Preview Controls) that will appropriately set all options for use with many other 3D programs. More configuration files will become available on the Pixologic website and in the ZBrushCentral forums in the future.
