Polygons: Fix Holes
Holes are sometimes introduced into a model based on how the data was created or due to removal of faces in order to correct issues, simplify
data or similar. In some cases, the original data was generated by means of placing different bodies in openings (for example the eyes in a figure
where the intention is to allow the eyes to be articulated). Whatever the reason, these openings generally need to be closed in order to
obtain a solid body.
Holes vs. Shell Bodies
One distinction to make is the difference between holes and bodies that represent a Shell. The two images below illustrate the difference.
Body considered a Shell
Body with holes
The first image above shows a hemisphere that can be considered a shell body. In this case, 'shell' simply means that there is no defined thickness
to it. The highlighted edges can be used to close the hole and thereby converting the body into a solid, however, it needs to be also considered that
the body should remain thin (so more like a cup than half a ball). If the thickness is to be (mostly) maintained, then using the hole-closure
tool is incorrect and rather the body should be Inflated .
For the second case, the head with the eye sockets each forming a edge loops that are separately closed, it is more likely that the intent is to
close these sections by generating new faces that fill in the space. In this case using the Fix Hole tool is appropriate and will result in a
shape that is more appropriate for the intended use.
Nevertheless, both Inflation (creating a thin but solid body) and Hole Closure (creating new faces to patch open edge loops) should be considered for
all cases that appear to have holes, depending on the end use of the file.