Just an opinion:
In my not so humble opinion, selecting numbers by incrementing/decrementing/scrolling is just a pain in the nether regions. I think it's just a leftover from digital clocks, where there was no keypad.
While not as cool looking, I would prefer a keypad every time (possibly suppleanted by an input mask). Entry is faster, requires less clicks, simpler to understand and generally more intuitive.
I've made some applications with time entry, and I've got nothing but praise from the users for using a simple keypad entry, instead of some more fancy looking, but more awkward to use input method.
If I were you, I'd rethink my solution. Compare the number of clicks needed and time needed to input the coordinates, the dexterity needed for the slider, and also how intuitive it is.
Please don't take this personally, this is just a pet peeve of mine, and I see it time and time again in various apps.
Edit: Some decent defaults also help. For example, N/S and E/W can be set the same as the user's position, and in most cases, it'll be correct.