Grid and Transfer use of Photos

I went to the art museum in Barcelona today.  I was told it wasn't worth it. It was on so many different levels.  Anti war show from Franco and WW II.  

The whole 18th through 20th centuries stuff (really good Romanesque too) was off the hook great.  Artists who are as good as "canon" artists.

For me, a small hanging of photos that showed how some 19th century artists used reference photos with grid and transfer was super relevant for me.

Check out these academic drawings too.

Here are the references.