What is important in GBSBabel to save a gpx file in nmea format for locr GPS Photo?
GPSBabel is an excellent tool to convert various file formats used by different GPS data loggers into other formats like e.g. the nmea format. Having downloaded GPSBabel you can start and use it.

Converting gpx file into nmea format

GPSBabel in the command line

GPSBabel can also be used as command line program. As command enter

gpsbabel -i gpx -f my_original_track.gpx -x track,fix=3d -o nmea -F my_converted_track.nmea

Important is the -x track,fix=3d parameter of the entry. So do not omit it!
The gpx file will be saved in the nmea format, which then can be opened in the locr GPS Photo software.