How can I structure my undergraduate thesis to include two slightly different projects? I did a research internship/ co-op in my final semester (our uni gives the option to choose between that and staying on campus for project work under professors). There, I was a part of two slightly different projects, one completed and another ongoing. I am finding it really hard to come up with a direction on how to include both of them in my thesis.

A bit of brief into the work done: The main problem was to design a Content-Based Image Retrieval System. It mainly consists of three parts- User Interface(web development), Feature extraction and Similar Image Retrieval (Deep Learning). For the first project, we designed and developed such a system after reviewing established papers. I was responsible for the literature survey and designing the user interface. For the second project, we are designing a system based on Ontology and Deep Learning both. 

Although the problem statement is similar, both the parts have vast and different literature surveys. The proposed method, as well as conclusions, also differ.  While I was responsible for survey and website development in the first project(ie.software-based work), for the second one I am responsible for all research, design and development of the project (ie. research-based work).

What could be a possible coherent structure that includes both the projects in a single thesis?
Any help is appreciated!
Your thesis can be outlined 4 chapters as follows:

Chapter 1: General introduction and review of literature~ you can divide or combine in background, approach and hypothesis,statement of the problem, justification of the research, and objectives of the research. but both projects only have the same problem statement. so you can separate 2 big parts in this chapter and each part has various sections. 

Chapter 2: Your first project~ Exposing what you did in a logical way. This chapter is concise as you mentioned.

Chapter 3:Your second project~
3.1 Introduction 
3.2 Materials and methods 
3.3 Results and discussion
3.4 Conclusion

Chapter 4: General conclusions and recommendations for both projects conducted~ general conclusion, key innovation, recommendation and future prospects.

The best way to make sure that it had better get consultancy from your supervisor or a mentor who is an assistant of your supervisor.