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gx:Track and dynamic updates on ExtendedData

I'm looking to add new coordinates and associated data points to a <gx:Track> over a <NetworkControlLink> in Google Earth. I've seen many examples on how to create <gx:Track>s with <ExtendedData> and how to do <Update>s on generic <Point> objects, but I haven't seen many that discuss both. The closest thing I could find is this link, which almost hits the nail on the head: http://groups.google.com/group/kml-support-advanced/browse_thread/thread/0d2cbefd087d576e?pli=1

Unfortunately, this link didn't get any responses, and the original poster didn't provide his orig_track.kml file, otherwise I'd have been able to reverse-engineer what he was doing since he claims he discovered a solution.

Right now I'm defining a <Placemark> like this in a file test.kml:

<Placemark>
    <name>Target</name>
    <description>...</description>
    <gx:Track id="orig_track">
        <when>2012-05-29T22:45:00Z</when>
        <when>2012-05-29T22:45:10Z</when>
        <gx:coord>-84.396863 33.774566 285</gx:coord>
        <gx:coord>-84.396917 33.774474 285</gx:coord>
        <ExtendedData>
            <SchemaData schemaUrl="#schemaId" id="testID">
                <gx:SimpleArrayData name="sig_strength">
                    <gx:value>60</gx:value>
                    <gx:value>65</gx:value>
                </gx:SimpleArrayData>
                <gx:SimpleArrayData name="gps_lock">
                    <gx:value>true</gx:value>
                    <gx:value>true</gx:value>
                </gx:SimpleArrayData>
            </SchemaData>
        </ExtendedData>
    </gx:Track>
</Placemark>

I'm trying to update it by having a <NetworkLinkControl> object that looks like this:

<NetworkLinkControl>
    <Update>
        <targetHref>test.kml<targetHref>
        <Create>
            <gx:Track targetId="orig_track_10003">
                <when>2012-05-29T22:45:20Z</when>
                <when>2012-05-29T22:45:30Z</when>
                <when>2012-05-29T22:45:40Z</when>
                <when>2012-05-29T22:45:50Z</when>
                <gx:coord>-84.396992 33.774443 285</gx:coord>
                <gx:coord>-84.397078 33.774421 285</gx:coord>
                <gx:coord>-84.397188 33.774363 286</gx:coord>
                <gx:coord>-84.397316 33.774298 287</gx:coord>
            </gx:Track>
            <SchemaData schemaUrl="test.kml#schemaId" targetId="testID">
                <gx:SimpleArrayData>
                    <gx:value>60</gx:value>
                    <gx:value>60</gx:value>
                    <gx:value>65</gx:value>
                    <gx:value>65</gx:value>
                </gx:SimpleArrayData>
                <gx:SimpleArrayData>
                    <gx:value>true</gx:value>
                    <gx:value>true</gx:value>
                    <gx:value>true</gx:value>
                    <gx:value>true</gx:value>
                </gx:SimpleArrayData>
            </SchemaData>
        </Create>
    </Update>
</NetworkLinkControl>

I think my issue might be with how instances of <SchemaData> are referenced. If I'm not mistaken, the <Schema> defines what fields should be in an array, and when I define my <Placemark> above, I instantiate the array with <SchemaData>. I'm not sure how to grab the instance of the array I created and add elements to it using <Update> and <Create>. My <Schema> looks like this:

<Schema name="schema" id="schemaId">
    <gx:SimpleArrayField name="sig_strength" type="int">
        <displayName>Signal Strength</displayName>
    </gx:SimpleArrayField>
    <gx:SimpleArrayField name="gps_lock" type="bool">
        <displayName>GPS Lock Status</displayName>
    </gx:SimpleArrayField>
</Schema>

I hope this was clear enough to understand! Thanks in advance for any guidance you may be able to provide.

Solution

  • I would suggest using a MultiTrack instead of a track and Updating that (add new Track children to extend the GPS path).

    However, ExtendedData is another matter and I have not tested Updating this. If it does not work as you expect, leave a comment here on what happened and your updated code if applicable. Alternatively you can just Delete the ExtendedData and then re-Create it.

    You may also be interested in the blog post from Sean Askay at http://www.unchartable.com/2011/05/google-io-high-performance-kml-for.html (The relevant video at about 17 minutes in, and the post has a link to some demo code with a working track update example).