What is a good resource to learn about oriented matroids in the context of digraphs and optimization?

Question

I am interested in oriented matroids in the context of directed graphs and optimization. Unfortunately, I know very little of the topic. Is there a book, article or a resource that serves as a good introduction to oriented matroids, especially in the context of directed graphs? It's a bonus if the resource is suitable for an (under)graduate level course and is preferably even free.

Answer 1

These notes written by Winfried Hochstättler for an MAA short course on matroids look like a good, short, introduction. They also contain references to several longer references on oriented matroids.