I’ve been using Google Earth (GE) a lot recently for my amateur cartography addiction (it’s been a problem for over 40 years, GE is like crack to me ;-)). In the process I’ve hit upon a couple of tips that don’t seem to be widely mentioned. The first tip is a way to get the length of a path or a polygon perimeter. All you need to do is [Update for GE 5.2]
copy the object to the clipboard, paste it into this Google Earth Tool and, click calculate look on the Measurements tab of the objects Properties dialog
The second tip is a bit more complicated it’s how to change a polygon into a path. I created an area boundary as an unfilled polygon which seemed the right way to go. Later I discovered that a polygon blocks all the paths under its area from being clickable for the pop-up information balloons. So I wanted to change the polygon to a path so that the other paths within the boundary area still had their pop-ups. Searching around there where quite a few people who had accidentally created polygons while making a path and no solutions were given. A feature of GE is that if you move the end point of a path near to the start point, it snaps to the start point and becomes a polygon automatically. If that’s not what you wanted and you don’t notice before hitting “OK” you lose your path and there is no option in GE to undo it.
I figured that since GE files are simply XML you should be able to edit the XML to change a polygon to a path so I tried it and it works. All you need to do is right click the polygon and choose “Save Place As”. Change the “Save as type:” to “KML (*.kml)” give it a name and save it. Now open the file in a plain text editor, my current favorite is Notepad++. Simply change the <Polygon> tags to <LineString> tags and remove the <outerBoundaryIs> and <LinearRing tags>. After I had spent a fair bit of time testing out this solution I found the same solution in a Google Groups search. Lesson here for me, don’t skimp on the searches, always include groups and blogs if you don’t find a web search answer.