Open Source TOPO map/GPS software...

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RobFromRedland
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Re: Open Source TOPO map/GPS software...

Post by RobFromRedland » May 20th, 2013, 7:15 am

Just an FYI - you CAN save a track as a GPX file in MapSource - File/Save As and choose GPX. It defaults to save it in its own weird format, but does fine saving it in GPX format.

I was reading once where there was some sort of mathematical algorithm to help filter out chatter, although I've never seen any of the utilities use it. Maybe I should do some more research on that front. [Later...] I just did a little googling and found the result. It is called the "Ramer–Douglas–Peucker algorithm":

http://en.wikipedia.org/wiki/Ramer%E2%8 ... _algorithm

It is supposed to work pretty well (in theory). Maybe it doesn't work so well in practice, or maybe it is difficult to put the right parameters in to make it work well.

More googling found this phone app which uses that algorithm: http://www.gaiagps.com/

This page: http://www.gaiagps.com/acknowledgments talks about how it uses it.

More fun stuff to play with....
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retired jerry
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Re: Open Source TOPO map/GPS software...

Post by retired jerry » May 20th, 2013, 7:39 am

I looked at that wikipedia.

It recursively goes through the track. It looks at three adjacent points at a time. If the in-between point is less than some distance between a straight line between the 2 end points, it eliminates it.

That's what I do manually. The trick is to not eliminate real switchbacks. You want that elimination distance to be greater than the GPS chatter but less than what a switchback would be.

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Koda
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Re: Open Source TOPO map/GPS software...

Post by Koda » May 20th, 2013, 8:23 am

GPSies.com uses the Peucker algorithm to simplify your tracks. It has some basic controls like high/med/low… to filter your level of detail.

Here is a screen shot:
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Capture129.PNG
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kepPNW
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Re: Open Source TOPO map/GPS software...

Post by kepPNW » May 20th, 2013, 8:56 am

My feeling is that algorithm isn't designed for what we're talking about here. That one provides generalization of the sort used to simplify vector display on a screen as you zoom out. I suppose there are folks who would find that desirable in a GPS track, but I definitely don't. I want actual real detail, of the sort that algorithm is designed to remove. The software I use to look at tracks does the generalization, of that nature, as it displays them.

What I'm looking for is something that recognizes the spider-on-acid effect of successive reading bouncing around in a single spot. In this shot, my GPS (red track) was attached to my pack, which was sitting on the ground:
Capture.JPG
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RobFromRedland
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Re: Open Source TOPO map/GPS software...

Post by RobFromRedland » May 20th, 2013, 9:21 am

kepPNW wrote:My feeling is that algorithm isn't designed for what we're talking about here. That one provides generalization of the sort used to simplify vector display on a screen as you zoom out. I suppose there are folks who would find that desirable in a GPS track, but I definitely don't. I want actual real detail, of the sort that algorithm is designed to remove. The software I use to look at tracks does the generalization, of that nature, as it displays them.

What I'm looking for is something that recognizes the spider-on-acid effect of successive reading bouncing around in a single spot. In this shot, my GPS (red track) was attached to my pack, which was sitting on the ground:
I'm looking for EXACTLY the same thing you are. Without having to do it manually. Even if something were to get me 80% of the way there I would be happy. I'm not looking for EXACT tracks, but something reasonably close to being accurate, without the drift. (or "spider-on-acid effect" - I love that depiction!)

Just curious - have you taken that track that you list and run it through the GPSies to see how the different levels of simplification affect the track? It would be interesting to see one map with the same track in different colors that had been run through the tool to see how they differ. I'm not sure I have any tracks that I haven't cleaned up so I can do that. The one you posted would be a GREAT one to try.

I also found this tool: https://sites.google.com/site/trackreducer/home

Does the same thing, however it allows you to specify the tolerance value so you can experiment and see what works well.
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kepPNW
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Re: Open Source TOPO map/GPS software...

Post by kepPNW » May 20th, 2013, 9:30 am

RobFromRedland wrote:Just curious - have you taken that track that you list and run it through the GPSies to see how the different levels of simplification affect the track? It would be interesting to see one map with the same track in different colors that had been run through the tool to see how they differ. I'm not sure I have any tracks that I haven't cleaned up so I can do that. The one you posted would be a GREAT one to try.
I haven't, but I'd be happy to try. I'd like to see exactly what it does, too, on a track I was very familiar with. The beauty of that one is I have three different units all recording the same hike, so it's a great one for comparisons.

I got very disappointed in GPSies, very quickly, though after first signing on there. I found they totally ignore the timestamp in the GPX files! Wrote the author/owner, and he said that most tracks he'd ever seen didn't have them, so, in a few words, "tough luck." I just couldn't imagine a more ignorant response, and pretty much never went back.

So, if I were to try this, does it offer you a SaveAs on the smoothed track? Or do I need to upload it three times under different names? Or...?

Thanks!
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Koda
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Re: Open Source TOPO map/GPS software...

Post by Koda » May 20th, 2013, 9:50 am

This is exciting because that is also exactly what I am interested in deleting too… this “spider on acid effect” (nominate that term for PH's phrase of the year…)

I would like to suggest starting a new thread dedicated to this subject. Not so much for thread drifting, but because I think it’s a valuable subject that will yield solutions that should be found on its own subject line later. I wish I knew the technical term for the Acid Spider effect, but a subject like “simplifiying static track point errors” or maybe just simply “editing track points” would be best.

I’d start the thread but am typing from my phone right now….
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MarsIsCobra
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Re: Open Source TOPO map/GPS software...

Post by MarsIsCobra » May 20th, 2013, 9:59 am

RobFromRedland wrote: I'm not looking for EXACT tracks, but something reasonably close to being accurate, without the drift. (or "spider-on-acid effect" - I love that depiction!)
Koda wrote:This is exciting because that is also exactly what I am interested in deleting too… this “spider on acid effect” (nominate that term for PH's phrase of the year…)
(sorry a bit off topic - or maybe not as it seems to be a developing meme here)

Spiders on acid. One of my favorite youtube videos. You need to give it 60 seconds before making judgement. Work safe, at least I think so, though I usually fall off my chair laughing every time i watch it. Moderator can delete if its just too far off topic or inappropriate. Or if other users disapprove, let me know. I'll delete it.


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retired jerry
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Re: Open Source TOPO map/GPS software...

Post by retired jerry » May 20th, 2013, 10:54 am

sort of like videos of cats or dogs being cute or chasing laser pens :)

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kepPNW
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Re: Open Source TOPO map/GPS software...

Post by kepPNW » May 20th, 2013, 12:03 pm

MarsIsCobra wrote:Work safe, at least I think so, though I usually fall off my chair laughing every time i watch it.
I have my hand clamped firmly over my lips, ... Must not part them... :lol:
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