Free Geography Tools

Last year, Google added the capability to embed time data into a KML file, allowing you to create animated time-based data displays and animations (like the examples on this blog on sea level rise animation, or converting animated GIF files into Google Earth animated images). Oddly enough, almost a year later you still can’t add time data to a KML file in Google Earth itself, but have to add it manually using a text editor, or in some limited ways when creating the file. But it’s not a particularly-complicated process, involving adding a few lines of KML code after Feature element tags; examples of Features are:

• <Folder>
• <Document>
• <Placemark>
• <GroundOverlay>
• <ScreenOverlay>
• <PhotoOverlay>
• <NetworkLink>

The two time-related KML elements are TimeSpan and TimeStamp.

TimeSpan: For a set of data that encompasses a specific interval between two times, you would use the <TimeSpan> KML tag. For example, for a period spanning from August 1, 2000 to September 1, 2003, associating the time data with a <Document> tag would look like this:

<Document>

<TimeSpan>

<begin>2000-08-01</begin>

<end>2003-09-01></end>

</TimeSpan>

The rest of your Document data, followed by the </Document> tag to close it …

For a time period running from a specific start time to the present, you’d just need the <begin>…</begin> part, and leave out the <end>…</end> section; similarly, for a time period running from the indefinite past to a specific time, keep the <end>…</end> section and leave out the <begin>…</begin>.

TimeStamp: For a set of data associated with a specific time, you would use the <TimeStamp> KML tag. If the data in your KML folder is valid for June 6, 1944 at 6 AM:

<Folder>

<TimeStamp>

<when>1944-06-06T06:00:00></when>

</TimeStamp>

The rest of your Folder data, followed by the </Folder> tag to close it …

All of the details for these two time-related KML tags can be found at Google’s KML 2.2 Reference Page, including the proper formatting for date, time, and timezones.

Time data is easy enough to add to a KML file, I suppose, but it would be nice to be able to assign them to a feature directly in Google Earth, for those who don’t want to deal with editing KML files. I suspect that will be added to Google Earth sometime in the future, especially now that ArcGIS Explorer has come out with superior time-handling features, but until then I’ve created another option. In upcoming posts, I’ll describe a simple utility I’ve written that lets you add time data to a Google Earth KML file without having to know any KML.