2

I have a Garmin Nüvi GPS and it's filled with XML records that look like this:

<trkpt lat="38.900207" lon="-77.008990">
<ele>11.67</ele><time>2013-06-11T04:04:49Z</time>
<extensions>
   <gpxtpx:TrackPointExtension><gpxtpx:speed>6.86</gpxtpx:speed> 
   <gpxtpx:course>271.06</gpxtpx:course>
   </gpxtpx:TrackPointExtension>
   </extensions></trkpt>

(line breaks added for legibility)

My question — what are the units for gpxtpx:speed ? I've examined all of the trackpoints for my GPS and the gpxtpx:speed never gets much above 30, and I KNOW that I'm going faster than 30MPH.

I've scanned the documentation and I can't find what the units are.

  • 3
    meters per second (m/s) see topografix.com/gpx_manual.asp#trk if you get to 70mph (112.7kph) you will see it going over 30 m/s (31.2928). – Mapperz Oct 13 '13 at 3:50
  • Hm. I guess it is documented in the Garmin schema. – vy32 Dec 18 '15 at 21:56
2

There are a few speeds that can be immediately tossed out:

30 ft/s = 20 mph < 30 mph
30 km/h = 19 mph < 30 mph
30 yd/s = 61 mph > 30 mph (not exactly a standard measurement)

The only other "common" speed I'd say is m/s, which works well:

30 m/s = 67 mph > 30 mph

If you can confirm that elevation is given in meters (it looks like it is for that particular point), that would be a nod towards m/s.

  • your assumption is correct. – Mapperz Oct 13 '13 at 3:51
  • Yes, I've gone through all of the data and it all seems to be in m or in m/s. It's odd that it's not documented anywhere, not even on the Garmin schema – vy32 Oct 13 '13 at 4:19
2

it is documented here: http://www8.garmin.com/xmlschemas/TrackPointExtensionv2.xsd.

<xsd:element name="speed" type="MetersPerSecond_t" minOccurs="0"/>

and type MetersPerSecond_t is defined as

<xsd:simpleType name="MetersPerSecond_t">
  <xsd:annotation>
    <xsd:documentation>
      This type contains a speed measured in meters per second.
    </xsd:documentation>
  </xsd:annotation>
  <xsd:restriction base="xsd:double"/>
</xsd:simpleType>

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.