How to convince and/or ask researchers to share data?
First, I suggest you to be very clear with what you are working on (which is not evident to me yet), what is your  deliverable, your time schedule, and why the data they have are important for your project.

Then, there always is something you can offer in return, that may have value for them: from a bibliographic report to innovative mapping of the data. Many people work at nice data vizualization tools that rock. Just saying, because you were talking about GPS data. We have entered a world of data science, where you can do a lot with novel tools. 

Whatever the option, I would suggest to take some data you have, work on some awesome analysis method, and sent them as a pre-gift