Polygon Repairs: Normals
Time to read: ~2 min
The Normals-Repair tool helps in the alignment (reversal) of individual surfaces within a body. Some applications do not explicitly consider which side of a triangle/facet
is inside the body and which is outside. Without knowledge of which side is considered to be on the outside, a number of internal processes will not be able to correctly
perform their functions.
Visually, normals are not directly represented, but if there are sections of a body that are displayed in a dark grey manner, then this is likely due to the Normal vectors of
those surfaces being incorrect.
Process
There are no user-options and the tool runs completely automatically when requested. Internally, it attempts to determine one surface that is 'correct' and then propagates
this orientation to all others. In general, this approach is robust, but if there are too many other issues in the data, then this may fail or fail to correct all issues.
In the case that the entire data becomes uniform, but uniformly incorrect (dark grey), the possibility exists to manually 'flip' all surfaces to point in the other direction.
This is done by selecting the body and then right-clicking to bring up the tool menu and using the "Flip Normals" option.
Option: All, Selected, Preview, Clear & Apply
Use of Preview and Apply are simply a way to generate a copy of the data before the process is started. In the case of the Preview option, the
process does not make a permanent change to the data whereas Apply does. As the data is stored in memory until it is either applied or deleted,
it is recommended to always use the Preview option. Use of the option to perform the functions either on a selected-bodies or all-bodies basis
depends on the intended use and whether multiple parts have been loaded.