Author Topic: Changing the start and finish points to an existing track  (Read 1094 times)

Changing the start and finish points to an existing track
« on: August 04, 2017, 09:57:08 pm »

Is it possible to change the start and finish points to an existing gpx track?

I'm wanting to ride the LEL route as a DIY but start and finish up north.


cameronp

  • upside down
Re: Changing the start and finish points to an existing track
« Reply #1 on: August 05, 2017, 04:39:14 am »
If you're just talking about "rotating" the track so it becomes Edinburgh-London-Edinburgh, that should be fairly straightforward. Many of the online mapping sites (e.g. RideWithGPS is my default recommendation) will let you upload a big GPX, cut it into pieces, and save it back out. There are also tools to stitch GPX tracks together. (In a pinch, some copy/paste work using Notepad will work - GPX is a simple text format.)

In the particular case of LEL, it's even easier, because the route is published as several separate GPX files, one for each leg between controls. You could ride them in whatever order you choose.

Making more detailed changes to a GPX track is not necessarily easy, because a GPX track doesn't retain information on where the control points (in the general sense of "go here then here then here", not the Audax sense) along the route are. If the route was made using an online mapping site you've got a good chance of being able to make your own copy and editing it using that site's tools, though.

Re: Changing the start and finish points to an existing track
« Reply #2 on: August 05, 2017, 08:54:36 am »

I've not decided where I'm starting yet. But possibly Pocklington or Louth.
The plan was to upload the gpx files to a site which will stitch them all together so I can submit it as a DIY. But I just need to change the start and finish before I can do that. Is that something which can be done in RideWithGPS?

As you say, en route I can use the existing files but in the order I decide to ride.

Thanks for the reply.


frankly frankie

  • I kid you not
    • Fuchsiaphile
Re: Changing the start and finish points to an existing track
« Reply #3 on: August 05, 2017, 09:56:03 am »
When stitching tracks together it is best if they are not timestamped, or failing that, if precautions are taken to keep the timestamps in correct sequence.  I don't know for sure about RWGPS, but most planners export timestamped tracks.  When tracks are joined in a way that creates a backward jump in the timestamps - most software will tolerate this but some GPSs may not - may freeze or otherwise misbehave. 
When in doubt I would run the file through a utility to strip out the timestamps - for a DIY submission that is OK (with the added benefit it makes the file smaller).  If you then wanted to use that file in an Edge you'd probably want to find another utility to re-stripe it - but you can just use the individual per-leg files anyway, probably better.
"This is a complex subject, with a need for more than one highlighter pen."

Re: Changing the start and finish points to an existing track
« Reply #4 on: August 05, 2017, 03:29:35 pm »
Yes, I only want to stitch them together to submit the DIY.
Still don't know how to alter the start/finish once they're stitched.

frankly frankie

  • I kid you not
    • Fuchsiaphile
Re: Changing the start and finish points to an existing track
« Reply #5 on: August 05, 2017, 04:13:39 pm »
The question doesn't really compute.  A Track is a long list of points.  The first one listed is the start.  The last one listed is the finish.
"This is a complex subject, with a need for more than one highlighter pen."

Re: Changing the start and finish points to an existing track
« Reply #6 on: August 05, 2017, 05:43:31 pm »

OK, so I've just stitched the north and south together and saved as a track. So I guess I submit that with my alternate start/finish?


Phil W

Re: Changing the start and finish points to an existing track
« Reply #7 on: August 14, 2017, 07:35:24 pm »
You need to join all the tracks bits you need together. Then split the tracks at the points you require. Then rejoin in the new sequence you require.

In Basecamp.

So take LEL north assuming you will ride north first.
Split it where you want to start.
You now have two tracks
One will be still be called LEL north (the first part of that track before the split) and you'll have a new track called track-n (the second part of the original LEL north track after the split)
Join track-n to LEL south in that order.
Another track appears track-m
Join track-m to LEL North in that order.
Another track appears track-l

Track-L is the new track starting and finishing at the new location you want.

You may wish to split LEL south as well so you end up with two tracks starting and finishing at your new start point. One track north to Edinburgh and back. One track south to London and back. You get the idea.