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Hi I was using JOSM, trying to average out GPS tracks so that I can align them with aerial imagery and then get to realign some roads. The problem I am facing is that when I download the GPS tracks, I see some clear lines of dots interconnected and a bunch of dots which are not interconnected (but I can mentally trace a line connecting them, they just don't appear on JOSM as connected). Let's call them simply lines and dots, respectively. Should I trust more the dots or the lines? Why does JOSM seems to give more relevance to the lines, since I have to mark the checkbox on the display settings to make the dots appear big and otherwise they are almost invisible when over imagery? Also, when displaying more info on the GPS data, e.g. velocity, only the lines (or the dots that compose the lines) get colored. Why that is? |
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GPS traces are essentially a list of points in a specific order, with timestamps for when they were recorded. The lines joining the points don't themselves contain any information (but can be used to show calculated speed etc.). Users uploading GPS traces to OpenStreetMap can choose how much information is shown to other users so some traces will only display as scattered points. If there are enough points in the area, JOSM's "heatmap" style display can help give an indication of the "most likely" path for the way you are looking at. Thanks for the link! Didn't know about that. On JOSM's heatmap (if that's the one you activate under Edit > Preferences > Display Settings > GPS Points > Track and Point Coloring > (radio button) Heat Map), it's kind of a shame it just calculates a heatmap for those points which also get a line drawn and not for those who get displayed as scattered points. I realised that because on a roundabout (focus on it on JOSM to see what I mean), there is no heatmap for the points that go southeast -> north, but only for those who go north -> southeast (the traffic goes anti-clockwise), which are also the points that get a line drawn. That's just how JOSM works or I'm doing something wrong? Thanks in advance for your patience, I'm a newbie on JOSM.
(13 Feb '19, 01:51)
dhiegov
I hadn't noticed that, the "points instead of lines" button doesn't seem to help either. The "combine tracks of this layer" item in the right click menu of the downloaded gpx data layer seems to give the desired effect though.
(13 Feb '19, 21:34)
InsertUser
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GPX files only contain dots. If there are timestamps in the GPX file, the software can deduce the direction in which the dots where traveled and how fast the person recording the file was moving.
So the lines and the dots are equivalent, the only difference is that the lines have timestamps?
Other way round the dots (waypoints) are the recorded position and time stamp. The lines just join up the dots. From the info on each dot software can work out the direction and speed of travel to the next dot.
Thank you, BCNorwich, but with "lines" I meant the dots which get lines that join them in JOSM, not the lines themselves. Sorry for making things a bit confusing. In the context of the question, I tought the terms were clearer.