Different distance comparing MyTracks and Google Earth for exported KML file

[GoogleCodeExporter]

What steps will reproduce the problem?
1. Record a track and note the distance reported in MyTracks 
2. Export track to gpx or kml file.
3. Upload file into Google Earth to see different distance than reported by 
MyTracks.

What is the expected output? What do you see instead?
Distances don't match.

What version of MyTracks are you using? On what version of Android? On what
phone?
MyTracks 1.1.11, Android 2.3.3, Motorola DroidX

See this track exported from phone. Track says 4.7 miles but Google Earth shows 
4.39 miles for KML file.

Original issue reported on code.google.com by ChasDCal...@gmail.com on 20 Nov 2011 at 5:28

Attachments:

• [2011-11-19 Eye Of Sandias - Mano Loop.kml](https://storage.googleapis.com/google-code-attachments/mytracks/issue-640/comment-0/2011-11-19 Eye Of Sandias - Mano Loop.kml)

[GoogleCodeExporter]

Original comment by nage...@google.com on 9 Dec 2011 at 11:15

• Changed state: Assigned

[GoogleCodeExporter]

I'm surprised this is an open issue because you wouldn't expect the distances 
to match. I loaded the 2011-11-19 Eye Of Sandias - Mano Loop.kml  file into 
Google Earth and it wasn't a path, so didn't have length. Removing the 
<MultiGeometry> tag turns it into a path and Google Earth reports the path 
length as 4.57 miles which is not the 4.39 miles stated in the issue. How did 
this data get the <MultiGeometry> tag?

Importing the data into My Maps gives a total length of 4.36 miles which is 
probably the closet to correct. Google Earth calculates distance by summing 
distance between points but the points you get in Google Earth depend on how 
the data gets imported. If its imported as a GPX file the import process will 
delete points that are too close together. I'm not sure what the threshold is 
but when I record data at 1hz I find a point for every second while moving and 
several seconds between points when stationary even though the GPX file had the 
data while stationary. When kml data is imported into Google Earth it doesn't 
get decimated. My Maps keeps all the points but the algorithm for calculating 
track length is not the sum of the distance between points. My Tracks is poor 
at estimating track distance because it just sums the distance between points 
to get distance and this issue is much discussed in the forums .

Original comment by kenep...@gmail.com on 19 Dec 2011 at 10:55

[GoogleCodeExporter]

Original comment by jshih@google.com on 21 Dec 2011 at 2:31

[GoogleCodeExporter]

Thanks Kenep. I re-exported my track from my phone into both kml and gpx files 
and opened them with Google Earth. Big differences. I can see where the gpx 
file deletes lots of points compared to kml file. Here's the distances: 
MyTracks app reports 4.70 miles. 
Google Earth kml: 4.43 miles according to elevation profile.
Google Earth gpx: 3.99 miles.
I guess I'll assume middle value is closest to actual.

Original comment by ChasDCal...@gmail.com on 21 Dec 2011 at 3:10

[GoogleCodeExporter]

Every GPS point has error. If the points are too close together the error is 
large compared to the distance covered and error perpendicular to the path 
always increases distance.

The My Tracks app uses points it doesn't save to calculate the total distance 
so it is the worst because they are often too close together. 

The kml file is every point My Tracks saved in the database. In calculating the 
total distance Google Earth will sum the distance between points. The GPX file 
is also every point in the My Tracks database but the Google Earth import will 
delete values from the GPX file it thinks are too close together which improves 
accuracy. 

If you upload your kml file to Google My Maps it sums the distance between 
points and applies an algorithm to reduce distance depending on distance 
between points. It will be the most accurate in most circumstances.

Original comment by kenep...@gmail.com on 22 Dec 2011 at 6:36

[GoogleCodeExporter]

As stated, when calculating distance in real-time, My Tracks uses all the GPS 
points, but can only save a sample of the points to the database.

When exporting as KML or GPX, My Tracks export all the points in all the 
formats.

Original comment by jshih@google.com on 23 Jun 2012 at 12:21

• Changed state: Intended