Custom URL logger to OwnTracks with speed in km/h

[flyingOwl]

I'm using GPSLogger as a client for my OwnTracks recorder server. I prefer GPSLogger because the android app for OwnTracks is more focused on location sharing and is also not able to log everything to a gpx file.

I use the custom URL logger in POST mode, pointing to the /pub endpoint of my OwnTracks server. The HTTP payload (json):

{
    "_type": "location",
    "lat": %LAT,
    "lon": %LON,
    "vel": %SPD,
    ...
}

It works like a charm, with one totally unnecessary problem: The OwnTracks ecosystem expects the velocity in km/h. They might have reasons for that. But for now, GPSLogger and OwnTracks are incompatible because neither of them is configurable.

I decided to open this issue here because (a) the OwnTracks ecosystem does not really encourage using a third-party app and (b) GPSLogger already works well with custom setups.

I have two ways in mind that I could implement to make this work:

1. Add another variable to the custom URL logger like %SPEED_KMH (%SPD_KMH would probably not work, as replacing %SPD might run first, right?). This would be a very small change. Though, having different variables for different units might clutter this functionality.
2. Add a setting for the custom URL logger to make the unit configurable. The setting could include "m/s", "km/h" and maybe even "mph" or "knots". And depending on what the user has selected, %SPD will be replaced by the converted value.

Tell me what you think about this. I tend towards the second option. But no matter what we decide, I can implement it and open a pull request afterwards.