'How accurate is it possible to track the moving speed of a person via an app when using React Native as an framework?

I wanna create an app for tracking the running speed of an person in intervals. I want to develop the app with React Native for primary IOS and eventually Android use. Are there any good frameworks available? Is it even realistic to develop something like this? I know of IOS that you can get as an developer via GPS only the approximate location of the user that would be not sufficient. I expect that through Internet signal it is possible to get a much more accurate position.



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