Many trails and custom maps are not yet available digitally and the process of scanning and absorbing them into existing GPS infrastructure is difficult and tedious. URhere.io is a simple, free and non-profit solution. A webapp usable with any smartphone that works offline and functions like any other app you would download from an app store.
Snap or upload a picture of any map or trail
Sync two points with satellite imagery
Trigonometry estimates GPS location on image
Non-Profit & Fully Open-Source on GitHub
Simply take or upload any picture of a map, synchronize two points with satellite images, and see your live, updating location on your map image. The premise is based on the foundations behind how next generation quantum compasses work but is actually much, much simpler. As latitude and longitude are essentially coordinates on a cartisan plane, we compare these to pixel coordinates on your image. We can then estimate where your current location is by simple triangulation. Free & Open Source on GitHub