How do you use this reference ?

[anuloma_viloma]

Hi,

How do you use such references with these red lines ?

http://www.uwm.edu/People/felchlin/photos.html

Thanks in advance
Hervé -

[anuloma_viloma]

Here is the picture
http://www.uwm.edu/People/felchlin/plains.jpg

[daarken]

the red lines are showing the different plane changes in the human figure.