If you want a hassle free way of geotagging your photos, plugging in a GPS module into your camera is the best way to go. Coordinates are stored in the photo's meta information as soon as you take it, no additional post-processing required. However, Nikon's original GPS module, the GP1, is quite expensive with a price tag of about 260$. That's why I've decided to build a low-cost DIY version which performs exactly the same but uses much cheaper components. The full building instructions including schematics and PCB layout for the DIY module can be found in my nikon-gp1-diy repository on GitHub. The assembled module is extremely small and fits perfectly onto the camera body thanks to a hot-shoe mount. Just plug it in, wait for a GPS fix and start shooting photos, it couldn't be easier than that! The total cost for the DIY module is roughly 40$, much cheaper than any commercially available alternative that I'm aware of.