in reply to Re: Data visualisation.
in thread Data visualisation.
Did you check if the data conforms to the Triangle_inequality ?
If not I doubt that any sane visualization is possible.
well at least with straight lines...
... but I fear with curved lines it might always be possible but not usable!
Cheers Rolf
( addicted to the Perl Programming Language)
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Re^3: Data visualisation.
by roboticus (Chancellor) on Jan 02, 2014 at 15:14 UTC | |
LanX: No, I didn't think to do that. It's a trivial check, so when I get home, I'll try to remember to add that. (Unfortunately, the security restrictions at work make it extremely difficult to actually do any coding.) Update: I've now added the triangle inequality check in the version at Re: Data visualisation.. Update 2: There was an error in my triangle inequality check (it didn't affect my original results, because my code didn't use any of the invalid triangles--by luck, not design). The error was that I only made one of the three checks required. The new check function is:
I also added an exhaustive check at the end:
The exhaustive check gives the following misses:
...roboticus When your only tool is a hammer, all problems look like your thumb. | [reply] [d/l] [select] |
by LanX (Saint) on Jan 04, 2014 at 09:38 UTC | |
> triangle inequality check Already a visual test reveals that projecting the data into 2D wouldn't make sense:
27 + 47 = 74 < 77
Cheers Rolf ( addicted to the Perl Programming Language)
updates
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by roboticus (Chancellor) on Jan 04, 2014 at 21:44 UTC | |
LanX: Yeah, my original triangle check was faulty. I only checked one case, rather than all three. Using your data, I had only a 1/3 chance of detecting that particular triangle as failing the inequality: 47 < 27 + 77 : Passes 27 < 47 + 77 : Passes 77 !< 27 + 47 : Fails... Since I only checked one case, I'd've missed a bad triangle. But my code didn't check all that many triangles, either, so it missed anyway. So I added an exhaustive check just for the helluvit. I've updated the node above accordingly. ...roboticus When your only tool is a hammer, all problems look like your thumb. | [reply] |
by BrowserUk (Patriarch) on Jan 05, 2014 at 03:26 UTC | |
by roboticus (Chancellor) on Jan 05, 2014 at 06:42 UTC | |
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by LanX (Saint) on Jan 06, 2014 at 10:22 UTC | |
> Update 2... The exhaustive check gives the following misses: wow ...indeed "a mess of bad triangles". TSP publications reach back to before the 1950s and IIRC the data was mostly taken from German or Swiss cities. 17 cities is a rather small and surely old example and I think at that time they just copied the kilometers from a tourist guide or train schedule or similar, w/o taking much care. So my theory was that just reaching the city limits naturally causes an error for large communities like Berlin or Zürich. But I don't think it's worth to try to correct this now with something like a fuzzy surface in the visualization, better try starting from the beginning with real coordinates. At least I think questioning the quality in my first reply was justified, it's worth checking data before trying to work with it.
Cheers Rolf ( addicted to the Perl Programming Language) | [reply] |