Google Earth Files - KML/KMZ
So, what are these KML and KMZ files anyway? They are Google Earth's file format for storing placemarks, network link information, and much more. I won't go into detail here, since there are excellent reference documents available from Google (see below). But, let me describe the fundamentals.
KML stands for Keyhole Markup Language (Keyhole was the name of the application before Google bought it and added their own features and larger databases). If you understand HTML/XML you will have little problem understanding the syntax of KML. You can learn about KML from the KML Tutorial, or get the full details from the KML Documentation.
KMZ stands for KML-Zipped. It is the default format for KML because it is a compressed version of the file. One of the more powerful features of KMZ is that it allows any images you use - say custom icons, or images in your descriptions - to be zipped up within the KMZ file. That way you can share these details without having to reference the files through some link to the Internet. For KMZ files without images, the file size will be much smaller than the equivalent KML file.
If you understand basic HTML/XML you can easily get started by saving a simple placemark you've created as a KML file (not the default KMZ), and looking at the resulting text file. If you are a programmer you will probably be fascinated by the topic of Network Links. Network links are one of the most powerful features of GE enabling a KML file to reference data dynamically on a server somewhere out on the Internet.
In a nutshell, learning to do things with KML/KMZ is the equivalent to learning to write a web page, but instead of a web page you are changing the face of the GE. Just like with web page creation tools, you don't have to know KML to create a KML file. You can start placing Placemarks or Image overlays straight from GE's interface.
What is GPX?
GPX (the GPS eXchange Format) is a data format for exchanging GPS data between programs, and for sharing GPS data with other users. Unlike other data files, which can only be understood by the programs that created them, GPX files actually contain a description of what's inside them, allowing anyone to create a program that can read the data within.
How can GPX help me?
GPX lets you exchange data with other GPS users, who might not be using the same software as you. Imagine the following scenario:
You're leaving for vacation tomorrow, and you wonder if anyone has some waypoint data for the tropical paridise you'll be visiting. You do a quick search on the web, and find a data file created by a GPS user who just returned from vacation!
You've found some GPS data you can use on your vacation! Perfect! Or is it?
You download the file, Vacation.txt from the vacation webpage, and try to open it with your GPS software. It crashes. Even though your GPS software reads and writes text files, this one is a bit different. You try making some changes by hand, but it's taking too long, and you're afraid you'll make mistakes. You do a quick web search to find a solution, but no converter exists. You end up printing out the text file and entering some of the waypoints into your GPS by hand. On the second day of your vacation, you realize that all the waypoints are off by a quarter mile. It turns out the website owner had his GPS set to a different datum, and you forgot to change your GPS before entering the data by hand.
You download the file, Vacation.gpx from the vacation webpage, and open it with your GPS software. You're surprised that it opens and transfers successfully to your GPS, since the file was created by a Lowrance GPS user on a Macintosh computer using a program you've never heard of. But since your GPS software supports GPX as well, you now have a complete, accurate set of waypoints for your vacation.
Feeling lucky, you wonder if there's a way to get the waypoints into your new street mapping software, so you can plan a route from the hotel. Your street mapping software doesn't support GPX, but maybe there's a converter available? A quick search on the web turns up another webpage! You wonder how much it's going to cost to buy a program just to do the conversion, but it turns out you don't even have to install new software - the webpage uses a FREE online form to convert your GPX file. You click the Submit button on the form, and your web browser launches your street mapping software with the converted data.
The next day, lying on the beach, you think about how easy it is for GPS programs to exchange data using GPX. While sipping a cool drink, you remember that anyone can write their own GPX converter to transform GPS data into a spreadsheet, a personal webpage, or a data file for their favorite program. And you think to yourself, "GPX really is a better way to exchange GPS data."
What are the benefits of GPX?
Here are some of the benefits that GPX provides:
* GPX allows you to exchange data with a growing list of programs for Windows, MacOS, Linux, Palm, and PocketPC.
* GPX can be transformed into other file formats using a simple webpage or converter program.
* GPX is based on the XML standard, so many of the new programs you use (Microsoft Excel, for example) can read GPX files.
* GPX makes it easy for anyone on the web to develop new features which will instantly work with your favorite programs.
What programs already support GPX?
Visit the GPX Resources page to get the latest list of applications and web services that work with GPX. If you don't see one of your GPS applications listed, write to the program author and ask them to support GPX in their next release.