When I was on university we had a PC application for creating geometrical drawings. As I already knew about software development at that time, I was very very impressed by that application.
Was 20 years ago, internet was not yet there at that time, but I did not forget about the program and you can still download it from the company which is developing and selling it.
The difficulty was finding out how to do the geometrical calculations! I never really had vector calculation in school. What I know about it is from some lessons on university. But I was able to find for most of the problems solutions. Some solved in this way, some solved in that way. Once I will come back and read a book about vector calculation and create a new library!
Some features are still missing from the original solution I worked with 20 year ago. But I am already very proud about what I were able to realize. When there is the next time slot where I have enough time, I will continue, for sure.