meaning of "round out" in this sentence

Hello friends,
I came across this sentence in my reading:

"In this chapter, we look at several disparate parts of this structures to round out our background knowledge."

What is the meaning of "round out" in this senctence?

I found these meanings in Oxford advanced learner's dictionary.

round something off (with sth):
or (round something out):

1) to finish an activity or complete something in a good or suitable way.
for example: She rounded off the tour with a concert at Carnegie Hall.

2) to take the sharp or rough edges off something.
for example: You can round off the corners with sandpaper.

Out of these two meanings neither seems to fit properly as the meaning of phrase "round out" in the concerned sentence. Please help me in deciphering the exact meaning of this sentence.
Thanks a lot.