The idea behind the DIY GPS logger is that you put it in your plane, drone, car or whatever, after your flight (drive) you remove the SD card (or connect via USB), upload the logfile to the NMEA to KML converter, download the resulting KML file and view the path your model took on Google Earth.
I used to use a "SkyRC GSM-015 GSS Speed meter". The problem with this is that it generates a proprietry file that can only be viewed in the SkyRC software. I did write a conversion program to convert this file to KML but SkyRC kept changing the file format between different firmware revisions and it was taking me too much time to keep re-writing the converter program.
While looking for alternatives online, I found an article on "RC Groups" by pesp with details of a homemade GPS logger he had made. It looked quite easy to build so i set about making my own. In his article pesp uses GPSVisualizer.com to convert the output to KML. I found this too restrictive so I wrote another program to do the conversion. The output from the logger is a standard NMEA GPS text file so is quite easy to convert.
My DIY logger includes a voltage buck to provide a stable 5v supply from a 1S LiPo (3.7v) but it could also be powered from a 5v pin on a flight controller or BEC.
The build time for the DIY logger is around 10 minutes.
Instructions for building it are in another article.