So now I loaded up the first traces to OSM.

To translate NMEA to GPX I had gpsbabel on the list
before, but I want to thank smssm1 and mallok for their
advice.

With gpsbabel -help I found the correct parameters at once
and conversion was no problem. Same with upload of the files to
OSM.

But then I tried to edit my data with JOSM. I should have been
warned. It was called an expert tool. Surely I'm none.
I will have to RTFM before using it.

For my next traces I will reduce the Interval between GPS points to the
minimal time my device allows and keep the antenna looking up in the sky
all time.

Now I have these questions:

a) Is there a direct way to read out data from Royaltek RGM-3800 via USB from Linux? I like to pass Windows whenever possible.

b) Is there a suggestion or convention how to form the filenames and descriptions for the traces and files on upload to OSM?

bye
black_bike