Closed GoogleCodeExporter closed 9 years ago
Original comment by nage...@google.com
on 9 Dec 2011 at 11:15
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
Original comment by jshih@google.com
on 21 Dec 2011 at 2:31
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
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
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
Original issue reported on code.google.com by
ChasDCal...@gmail.com
on 20 Nov 2011 at 5:28Attachments: