KML ExtendedData opening up "wrong" popup in GE? - kml

Question

I notice certain behaviour using ExtendedData in KML which I feel renders the use of ExtendedData questionable, especially if the trackway crosses itself.
I would like to know if there is a fix or workaround?
GoogleEarth (v7.3.2.5491 (32-bit)) appears to do calculation on the fly to calculate the nearest waypoint to the clicked position. This is a problem if the nearest waypoint by crow-flies distance is further away along the trackway taking time into account. I have an MRE here...
<kml xmlns="http://earth.google.com/kml/2.2" xmlns:gx="http://www.google.com/kml/ext/2.2">
<Document xmlns="http://earth.google.com/kml/2.2" xmlns:gx="http://www.google.com/kml/ext/2.2">
<name>2018-08-27_Mon</name>
<Schema id="schema">
<gx:SimpleArrayField name="gps_coords" type="string">
<displayName>GPS Coords</displayName>
</gx:SimpleArrayField>
<gx:SimpleArrayField name="ping_time" type="string">
<displayName>Ping Time</displayName>
</gx:SimpleArrayField>
</Schema>
<Folder xmlns="http://earth.google.com/kml/2.2" xmlns:gx="http://www.google.com/kml/ext/2.2">
<name>Tracks</name>
<Placemark xmlns="http://earth.google.com/kml/2.2" xmlns:gx="http://www.google.com/kml/ext/2.2">
<name>Trackway</name>
<styleUrl>#my_track</styleUrl>
<gx:Track xmlns="http://earth.google.com/kml/2.2" xmlns:gx="http://www.google.com/kml/ext/2.2">
<altitudeMode>clampToGround</altitudeMode>
<when>1970-01-01T05:02:28Z</when>
<when>1970-01-01T09:04:00Z</when>
<when>1970-01-01T11:06:00Z</when>
<when>1970-01-01T14:59:30Z</when>
<when>1970-01-01T15:02:00Z</when>
<when>1970-01-01T17:03:11Z</when>
<gx:coord>-8.460239 54.253286 0</gx:coord>
<gx:coord>-8.460439 54.256286 0</gx:coord>
<gx:coord>-8.460639 54.259286 0</gx:coord>
<gx:coord>-8.467867 54.262505 0</gx:coord>
<gx:coord>-8.462653 54.256286 0</gx:coord>
<gx:coord>-8.460599 54.250317 0</gx:coord>
<ExtendedData>
<SchemaData schemaUrl="#schema">
<gx:SimpleArrayData name="gps_coords">
<gx:value>No 1. 54.253286 -8.460239</gx:value>
<gx:value>No 2. 54.256286 -8.460439</gx:value>
<gx:value>No 3. 54.259286 -8.460539</gx:value>
<gx:value>No 4. 54.262505 -8.467867</gx:value>
<gx:value>No 5. 54.256286 -8.462653</gx:value>
<gx:value>No 6. 54.250317 -8.460599</gx:value>
</gx:SimpleArrayData>
<gx:SimpleArrayData name="ping_time">
<gx:value>2018-08-27T05:02:28Z</gx:value>
<gx:value>2018-08-27T09:04:00Z</gx:value>
<gx:value>2018-08-27T11:06:00Z</gx:value>
<gx:value>2018-08-27T14:59:30Z</gx:value>
<gx:value>2018-08-27T15:02:00Z</gx:value>
<gx:value>2018-08-27T17:03:11Z</gx:value>
</gx:SimpleArrayData>
</SchemaData>
</ExtendedData>
</gx:Track>
</Placemark>
</Folder>
<Folder>
<Placemark>
<TimeStamp>
<when>1970-01-01T05:02:28Z</when>
</TimeStamp>
<description>Desc No 1. 54.253286 -8.460239</description>
<styleUrl>#waypoint</styleUrl>
<Point>
<coordinates>-8.460239 54.253286 0</coordinates>
</Point>
</Placemark>
<Placemark>
<TimeStamp>
<when>1970-01-01T09:04:00Z</when>
</TimeStamp>
<description>Desc No 2. 54.256286 -8.460439</description>
<styleUrl>#waypoint</styleUrl>
<Point>
<coordinates>-8.460439 54.256286 0</coordinates>
</Point>
</Placemark>
<Placemark>
<TimeStamp>
<when>1970-01-01T11:06:00Z</when>
</TimeStamp>
<description>Desc No 3. 54.259286 -8.460539</description>
<styleUrl>#waypoint</styleUrl>
<Point>
<coordinates>-8.460639 54.259286 0</coordinates>
</Point>
</Placemark>
<Placemark>
<TimeStamp>
<when>1970-01-01T14:59:30Z</when>
</TimeStamp>
<description>Desc No 4. 54.262505 -8.467867</description>
<styleUrl>#waypoint</styleUrl>
<Point>
<coordinates>-8.467867 54.262505 0</coordinates>
</Point>
</Placemark>
<Placemark>
<TimeStamp>
<when>1970-01-01T15:02:00Z</when>
</TimeStamp>
<description>Desc No 5. 54.256286 -8.462653</description>
<styleUrl>#waypoint</styleUrl>
<Point>
<coordinates>-8.462653 54.256286 0</coordinates>
</Point>
</Placemark>
<Placemark>
<TimeStamp>
<when>1970-01-01T17:03:11Z</when>
</TimeStamp>
<description>Desc No 6. 54.250317 -8.460599</description>
<styleUrl>#waypoint</styleUrl>
<Point>
<coordinates>-8.460599 54.250317 0</coordinates>
</Point>
</Placemark>
</Folder>
</Document>
</kml>
Clicking on the trackway midway between #4 and #5 pops up the ExtendedData for #3. Same with #5 and #6 resulting in #1 opening. It kind of makes senses because the trackway is just painted as the straight line between two points and does not have its own geometry. So, I could live with that even though a naive user might expect a precise popup for the intermediate positions. However, if I move the time slider to exclude/disappear points #1, #2, and #3, I would now expect #1, #2, and #3 to be excluded from the calculations. But this is not the case. The same results as above obtain. That is not what I would expect.
In this MRE it is not a problem as such but on a large trackway with several hundred points and the trackway going over and back across itself throughout the day, then such ExtendedData popups are, IMO, ususable.
To work around it, I have created a CDATA description for the each waypoint in the track which is acceptable
Is there a KML workaround for this behaviour or is it just the way GE implements it? Any other suggestions perhaps?
Liam

Answer 1

Google Earth Pro behaves in such a way that when clicking the segment of track past the mid-point gives the metadata for the next waypoint. This is what you are seeing when clicking on a track and seeing metadata for another point.
Also note the KML above does not conform to the KML 2.2 standard. Couple of validation issues.
There should not be any whitespace in the point coordinates. The whitespace should be replaced with a comma (,):
old:
<Point>
<coordinates>-8.460239 54.253286 0</coordinates>
</Point>
new:
<Point>
<coordinates>-8.460239,54.253286,0</coordinates>
</Point>
The namespace should be xmlns="http://www.opengis.net/kml/2.2" rather than the old form of http://earth.google.com/kml/2.2.
Some of the element are out of sequence. KML 2.2 has a strict order of elements (see reference) but Google Earth generally ignores the order of elements. The correct order of elements is as follows:
<Placemark>
<description>...</description>
<TimeStamp>...</TimeStamp>
<styleUrl>...</styleUrl>
<Point>...</Point>
</Placemark>