Messages

1

User Projects / Re: Quantum Physics - GPS replays

« on: May 24, 2010, 09:16:33 AM »

Doh!  Thanks for the pointer.

2

User Projects / Re: Quantum Physics - GPS replays

« on: May 23, 2010, 05:18:07 PM »

Hi Scott,

Your "ants" are pretty interesting.  How did you eliminate the track lines from the display to get just the moving dots?

3

Feature Requests / Simplification for multiple tracks

« on: July 26, 2009, 10:22:14 PM »

I do a lot of network analysis.  Over time, the networks end up having a lot of data points because the network merging algorithm tries to maintain all of the useful information.  I am aware of the track simplification capability, but it only works on a single track.  Many of my networks have more than 20 tracks within the network (some have a lot more).   It is a bit tedious to do this for each track individually.

Could you add the capability to apply the simplification to all active tracks?  This would allow me to simplify the whole network (or multiple networks) at one shot.

There is probably some complexity under this request.  Some tracks are traversed very frequently, so there are lots of points and a big simplification opportunity.  Other tracks may have been traversed only once or twice, so the number of points is sparse by comparison.  I would ideally like to have TopoFusion recognize the situations and apply more simplification where the data reduction is the greatest without introducing significant loss of accuracy.  So if I specify a number of points or a percentage reduction (another request), TopoFusion determines how to best meet this goal.

4

TopoFusion Pro / Merging into an existing network reduces data

« on: September 23, 2008, 10:23:30 PM »

You caught me.  My usual procedure is to read the data from the GPS using SportTracks, export to a GPX file and then read that into TopoFusion.  I don't know what the precision is that comes out of the GPS (Garmin Edge 305), but I am guessing that is what is being passed through SportTracks.

Your response got me to thinking.  Doing a bit of math reveals that a 0.000001 degree difference (6 digit precision) is not very much.   This translates into 0.1112 m (4.38 inches) for latitudes and 0.0885 m (3.48 inches) for longitudes for the trails I am riding.  12 digit precision suggests a resolution of about 0.1 microns...well under the accuracy of the GPS I am using and much more detail than I need!

Given the distances involved with 6 digit precision, I think it is good enough for my purposes.  Since I don't work at Microsoft, using less disk space is still a virtue.

I think the current solution is OK now that I know why the files sizes shrank so much and that I am not loosing anything that seems important.  Thanks!

5

TopoFusion Pro / Merging into an existing network reduces data

« on: September 19, 2008, 11:46:23 PM »

Thanks for looking into this.  I did not think about duplicate data.

The Original file was created very recently.  It is the result of merging about 36 raw GPX data files.  I don't think any trails had been added into this until I tried to add this new trail.  I re-ran the Network Analysis using v3.41 and had similar (but not exact) results to the previous merge.  With both v3.38 and v3.41, about 40% of the data points are duplicates in the network analysis result based on the full 6 digit precision values in the merged GPX file.  

I noticed that the original input data files from the GPS have 13 digit precision for latitude and 12 digit precision for longitude.  If the internal coordinates maintain this precision, the points will be different while doing the network analysis.  They are written out with 6 digit precision, so the next pass using the previously merged data could see these points as identical due to the loss of precision.  I investigated this hypothesis and it seems to be true.  The files generated by the initial network analysis not only have lots of duplicates (about 2/3 of the points in this case), but they are almost all in sequences of consecutive identical points.  Reading the file in again for an incremental network analysis significantly reduces the duplications and sequencing.  This result seems to fit the hypothesis of different precisions of the incoming coordinates.

The reduction in the number of points does not seem to make a large difference in the appearance of the track in the display.  However, I assume this may have some impact on merging more precise data from future GPS tracks and the parallel/face reductions while the algorithm is running (since the number of data points has been reduced and the minimal geometric distances have changed slightly).

6

TopoFusion Pro / Merging into an existing network reduces data

« on: September 18, 2008, 08:45:44 AM »

Alan,

Thanks for the fast response.

You're right: selected = loaded and enabled.  The data files are properly loaded and processed and the resulting tracks show the old and new data as expected.

Good point about the spurs, but I don't think the original data set had a problem there.  Also, since it was created by network analysis, those spurs would have been eliminated when it was created.

Thanks for the offer of additional help.  I'll send you the data files separately.

7

TopoFusion Pro / Merging into an existing network reduces data

« on: September 18, 2008, 12:26:19 AM »

I am a happy user of TopoFusion and use it several times a week to track mountain bike rides.  I have created a pretty good set of trail maps based on merging individual rides at each location using the Make Network capability.

I noticed something that seems odd.  I went on one of the rides I do pretty frequently and then did a network analysis using the new track (New) and the original merged data (Original) that was created using v3.38.  I had a short bit of new trail in the new track, but the vast majority of New is well represented in Original. In this case, Original is superset of New except for the short new track.  This is confirmed in when the New merged data is compared with Original.  However, I noticed that the New merged file is significantly smaller.  I checked a few things in the GPX files and found:

 Â                                          Original   New 3.38   New 3.41
File size                                3677 KB     1385 KB      931 KB
Waypoints ("<wpt")                   75             92            89
Tracks ("<trk>")                      103            115          109
Track Points ("<trkpt")           43152       16148       10582
TopoFusion #Points               43227       16240       10671

I read the June 2004 ACM paper and followed your explanation of parallel and face reductions.  As I understand the algorithm, the number of points is not reduced below the maximum number from the polyline with the most points when performing a parallel/face reduction.  Since serial reductions are always performed, the Original file should not have any points (vertices) of degree two.  Based on this, I would have expected New to be slightly larger (due to the points in the short new track) than Original, but by only a very small amount.  As the numbers indicate above, New was slightly more than 1/3 the size of Original using v3.38.  I installed 3.41 and the problem is even worse (or better, depending on your point of view) but it seemed to run much faster.

The procedure I used was to select the new track and Original and then run Network Analysis.  I did not do an explicit data reduction, spline or any other steps.  I am using the same reduction and contraction setup parameters in all cases.

Looking closely at the tracks suggests that using re-using a previously generated network does some sort of a spline because the New tracks are much smoother when I zoom in a lot.  This smoothing effect only occurs along the path of my most recent ride (the new track is smoother than the Original track).  If there is some sort of reasonable data reduction being performed, why wasn't this also applied when Original was generated?

Am I really losing resolution using a previous generated network as one of the inputs?  Is it safe to merge data using previously generated networks?