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Announce turns with negative value

7 Nov 2016
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Firstly congratulations on an excellent application.

I’m planning a bike ride of about 70km and want to limit the number of waypoints in my GPS. The “GPS route” is an excellent facility. What I wanted to do was get waypoints at each turn and for 60m before and after to show “mini” route on my GPS. When I set “announce turns” to -60 m the resulting waypoint seems to be a “projection” 60m on the “turn bearing” rather than 60m further along the route. Is this what you intended?

 Also in July you responded to a question on “uploading a gpx file into”. Any idea when this might happen?


Wed 9 Nov 2016, 17:37

Glad you’re finding the site useful!

How this should work is that it sets a waypoint on the route (the “polyline”, i.e. the actual line you’re following) 60 metres before the turn. Is that not what you’re seeing?

It might be interesting to check the downloaded file with a site that can plot GPXs/TCXs on a map, such as If that shows the waypoints where you’d expect them to be announced, great. If not, let me know what journey you’re trying it with, and I can take a look.

GPX file upload is almost finished and just requires me to spend a day or two on a few final aspects. Should be later this month, hopefully (together with a fun new elevation feature!).

Thu 10 Nov 2016, 07:49


Thanks for the fast response. By -60m I’m referring to after the turn point. Before the turn points acts as you described.

Yes I’m using GPS Visualizer. The journey is from Bentley to Portsmouth a road version of the Shipwright’s Way

Thu 10 Nov 2016, 13:53

I’ve just had a play with that using GPS Visualiser. For .tcx, it shows the full polyline, plus turn symbols 60m before the turn itself. For a .gpx track, it just shows the polyline. For a .gpx route, it just shows the turn symbols, 60m before each turn.

This is what I’d expect (though GPS Visualiser rather unhelpfully joins up the turn symbols on a .gpx route!). Which one of the three are you using, and what would you expect it to do differently?

Thu 10 Nov 2016, 14:36

Sorry Richard. I’ll try and explain my question more clearly.

I’m using gpx with GPs visualizer to display results.

Consider three points. The turn point B, point A, which is the “track” point before the turn point, and point C which is the “track” point after the turn point

Consider two further points . Point X is  60m before a turn, point Y 60 m after the turn: both on the route

Point X appears on the route (as far as I can tell) and is about 60 m from point B on the bearing from point A to point B .  This, I think, is what you were saying and what I’d expect.

If you were to project a line from point A to point B and then extend it 60 m beyond point B you get point Z appears to place point Y at the position of point Z and not 60m from point B along the bearing from point B to point C

Fri 11 Nov 2016, 16:23

Oh, I see! Yes, that certainly won’t work. The code ‘backtracks’ along the route to find the place 60 metres before the turn; there’s nothing in there to ‘forwardtrack’, if you see what I mean. I’ll think on how that might be achieved.

Fri 11 Nov 2016, 18:42

I’ve been playing around. I used GPS visualizer to convert the gpx file to a text file and include the bearings.

I then used a spreadsheet to convert gpx lat and long to OS Grid ref and found point X using the back bearing for point B (ie the bearing from B to A,) and point Y using the bearing from B to C.

Finally I converted OSGrid for X and Y back to lat and long and used visualizer to convert text file back to gpx for my sat nav.

Took a half an hour to set up the spreadsheet, but now it’s done the whole process only takes a few min to process a 60k route.

Anyway thanks for your help and advice and keep up the good work on the site