Anomalous distance data (goes backwards) in TCX da... - Fitbit Community

Anomalous distance data (goes backwards) in TCX data

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We're processing TCX activity data from a number of services and have noticed something odd in some Fitbit activities:

The <Trackpoint> <DistanceMeters> is a cumulative value, but in some cases it can seem to switch to zero, which as far as I can tell would be effectively undefined behaviour (or "unwind entire activity", which is not really a sensible interpretation)

A sample below (the Latitude and Longitude are the same in all three Trackpoint record, but have been replaced by Y & X to avoid leaking actual user data here)

In this case there were eight <DistanceMeters>0.0</DistanceMeters> at the end of the data

Thanks

                    <Trackpoint>
                        <Time>2018-10-11T07:49:02.000+01:00</Time>
                        <Position>
                            <LatitudeDegrees>Y</LatitudeDegrees>
                            <LongitudeDegrees>X</LongitudeDegrees>
                        </Position>
                        <AltitudeMeters>8.09698809067007</AltitudeMeters>
                        <DistanceMeters>6908.610000000001</DistanceMeters>
                        <HeartRateBpm>
                            <Value>145</Value>
                        </HeartRateBpm>
                    </Trackpoint>
                    <Trackpoint>
                        <Time>2018-10-11T07:49:06.000+01:00</Time>
                        <Position>
                            <LatitudeDegrees>Y</LatitudeDegrees>
                            <LongitudeDegrees>X</LongitudeDegrees>
                        </Position>
                        <AltitudeMeters>8.129266699657943</AltitudeMeters>
                        <DistanceMeters>6917.14</DistanceMeters>
                        <HeartRateBpm>
                            <Value>145</Value>
                        </HeartRateBpm>
                    </Trackpoint>
                    <Trackpoint>
                        <Time>2018-10-11T07:49:11.000+01:00</Time>
                        <Position>
                            <LatitudeDegrees>Y</LatitudeDegrees>
                            <LongitudeDegrees>X</LongitudeDegrees>
                        </Position>
                        <AltitudeMeters>8.225675101139828</AltitudeMeters>
                        <DistanceMeters>0.0</DistanceMeters>
                        <HeartRateBpm>
                            <Value>145</Value>
                        </HeartRateBpm>
                    </Trackpoint>

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