Better GPS track elevation data

Few weeks ago we made a nice little hiking trip near Pazin. I forgot my Garmin and recorded the trip with my Android smartphone. The resulting elevation graph was pretty strange. Look at the black line:

The blue line is the elevation computed from SRTM (Shuttle Radar Topography Mission) data.

Is it obvious why the Android elevations were strange? The first thing is that the graph was cca 40 meters above the actual elevation lines. But this isn't something that bothers me too much. Because if it were only this -- the actual elevation gain should be the same (but the maximum/minimum elevations would be wrong).

But the second thing is what was really strange. Android cooked up a hill in the first 700 meters of our trip. A big hill, almost 420m high. But in reality there was no hill there.

This is why I added an option "Add GPS track elevation" on Trackprofiler. It is online almost two months now. But the actual data used is raw-SRTM data. And that's why the resulting graph was sometimes not a smooth line but a succession of horizontal lines (Look at the blue line in the graph).

I've been experimenting with few different algorithms to make a better elevation graphs from NASA's elevation data. And I think I finally found a good approximation. The result is the red line:

This new (and better) algorithm for elevation detection will be deployed is on Trackprofiler soon now.

PS. I'm not sure but the fact that my Android elevations are cca 40 meters higher may be because of the deviation between the ideal geoid and the actual Earth surface. 

Add missing time on GPS tracks

It is easy to add new points on an existing track. Just click on the track and move the points marked with (or move the if you need to move existing points):

Those new points don't have the same metadata as the old ones. For example, new points don't have elevations. That's why the elevation graph looks like this:

There is a "empty hole" on the part of the track where the new points are. This is easy to solve: Just go to "Add elevation" and click on "Add missing elevations" and the result is:

By the way, you could use the "Add elevations" option instead of "Add missing elevations" if you want to override even the existing elevation data. 

But there still is one thing missing. Look at the analytics page, the speed graph:

Here, too, there is the same "empty hole", and that's because the new points have no time(stamps) saved

For situations like this I'm finishing/testing a new feature on Trackprofiler. When choosing it, the application will try to interpolate times for all points where the time data is missing. The interpolation is based on distances between points.

The "Add missing time" feature is almost ready and will be online soon is deployed now.  (BTW. Watch us on Trackprofiler on Twitter, Facebook or Google+ for notifications about the new versions deployed.)

Print only selected track elements

From now on, you can decide which elements to include when printing the track:

Feedback is welcome.

New layout for GPS track analytics page

There was a few deploys with loads of new features on trackprofiler in the last few months. This is the first of a series of blog posts covering new features introduced lately.

If you remember, the original "Track analytics" page was just a series of graphs. Yesterday a new version was rolled out with the new version:

For every graph you can see:

• Elevation graph
• Speed graph
• Steepness graph

For every graph by moving over it -- you can see exactly on the map where that point was recorder. 

See an example here.

GPS elevation graphs

This blog post is a short history on the evolution of GPS elevation graphs on trackprofiler.

When starting the service I created a simple javascript based graph library and used it for GPS tracks elevation graphs:

...but over time, some problems arose. First of all it was slow and rendered in the browser. That means that for slower computers the graphs slowed the rendering of the entire page by more than a second.

And, there was another thing I wanted to show on the graph -- the speed graph. So, a month ago a new version of TrackProfiler was deployed. The graph is now a PNG image created on the server -- no client's CPU is used. The graph, then, looked like:

The green graph is speed, the gray one is elevation.

But, there still was one thing in the evolution of the graph I wanted to make. For example on the GPS track shown -- it started on elevation 197m and never went below. So, it don't make sense to show the vertical  part of the graph from zero. It only makes the uphill and downhill slopes flatter.

After another iteration (online for the last 3 days) -- the vertical part of the graph now starts from the minimum elevation found on the graph. And the uphill/downhill slopes are better visible:

See an example here, or try it yourself on TrackProfiler.

Gpxpy version 0.8.0

Gpxpy is an open source python library for parsing and manipulating GPX files. It is one of the core parts of the TrackProfiler web site, and one of the open sourced parts of it. In the last few months a lot of work is done. Two new important features:

• gpxpy can now use lxml (if available) to parse GPX files (contribution from Isaev Igor)
• Python 3 support (contribution from Robert Smallshire)

...and many more small bug fixes and unit tests to make it faster and more stable.

It is licensed under Apache 2.0 and there should be no problems using it even with your own closed-source commercial apps.

PS. The original trackprofiler utility app and the library used to show analytics graphs (cartesius) are also open source.

Even more GPS editing tools

Even more GPS editing tools are available in the newest version of TrackProfiler. Those are:

• Remove time metadata from the track,
• Remove elevation metadata from the track,
• Elevation graphs are not shown if the track has no elevation data,
• Move graphs,
• Add/remove to elevation.

Plus, few bug fixes:

• Problem with embeding tracks whose subject contain non-ASCII characters,
• Default background for embeded tracks,
• Better handling for inbound emails for email track uploading.

Enjoy!

Track page load speed

Just rolled out a new update with a an important improvement. The problem was that the track page was generated entirely at the moment you requested it (i.e. you clicked on the link). This is a somewhat slowish process and consequently the page load speed was also slow.

Now parts of the page are cached and the page load speed is improved by 3-4 times.

Enjoy!

Embeding tracks

This month -- embeding GPS tracks from Trackprofiler in your site. It's easy -- when on the page with your track, just click the "Embed" tab. Then, copy the code on your page. There are 3 predefined widths for widgets, select the one that best fits in your page.

Here is an example of how it looks:

Export track stats to a CSV file

In the last two weeks I was hiking around my small city (Višnjan). I made a total of 737.96564616 meters uphill, 32575.07452042m long (32680.59386254m if counting elevation).

How do I know those numbers?

Because there is a new option in TrackProfiler -- You can export track statistics in a CSV file. For all files or for files with specific tags. All I did was to export in CSV files with tags "visnjan" and "hiking" and then computing the sum of columns with Excel.

If you tag all your hiking tracks with "hiking", tracks when you were in Italia with "italy" and Alps tracks with "alps" -- just enter "hiking italy alps" in the new CSV exporter form. The resulting file will contain data for all those tracks.