How To Make A Trail Map Using Google Earth
What You Need
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| The Garmin GPSMAP 60Cx that I used to make my trail map. It's a multipurpose GPS that I also use on my boat and in my car. |
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The Sony ICD-SX46 digital voice recorder that I used to take notes in the field. It seems to me that the unit is designed for right-hand operation, since the record and stop buttons are directly under your thumb. |
What you need:
- GPS receiver (perhaps including some accessories, see below)
- Digital camera
- Some way to take notes in the field (a digital voice recorder is handy)
- Google Earth Plus account
GPS Receiver
Here are some tips about what type of GPS receiver to use (I use a Garmin GPSMAP 60Cx):
- Position accuracy - I first tried using a old GPS that wasn't very accurate, but it was entirely inadequate. If the imagery is very detailed and you want your trail map to be very detailed, then your GPS track logs will have to be as accurate as possible. This means using a late-model GPS that has a sensitive 12-channel receiver that supports WAAS (Wide Area Augmentation System). I consider good sensitivity and WAAS to be essential, since walking through the woods can degrade GPS accuracy, especially walking through dense woods or down into a ravine. Many GPS receivers (including mine) use the SiRF chipset, which has a good reputation for high sensitivity even in difficult circumstances. Most GPS receivers now support WAAS, which is a system to improve basic GPS accuracy that was developed by the FAA for use in airplanes (but it works fine on the ground, too).
Speaking of accuracy, the nominal position accuracy when using WAAS is three to five meters 95% of the time, and typical accuracy is one to two meters horizontally and two to three meters vertically, all according to my Garmin manual. In my experience, this type of accuracy requires a clear view of the sky and good satellite geometry (where the satellites are positioned all over the sky so the GPS can triangulate its location more accurately). Walking in the woods, my typical accuracy was 15 to 25 feet, but it was occasionally worse than 30 feet (these are estimates based on my track logs).
- External antenna - I made all my track logs using the built-in GPS antenna, but to get the best reception you have to hold the GPS high up and away from your body. After a while this gets to be tiring. You can get as good or better reception using an external antenna, which allows you to clip the GPS to your belt for hands-free operation. The Garmin external antenna (GA 25MCX) is very small (about 1.75" square by 0.5" thick) and has a magnet in the base. As an experiment, I made a "GPS hat" by taping a big steel washer out of view under the top of an ordinary baseball cap, then attaching the antenna to the top of the hat using its magnetic base. Although I looked more than a little geeky with an antenna on my head, it significantly improved the signal reception. During a test with moderately good sky visibility, the Estimated Position Error (EPE) was about 15 feet using the built-in antenna and about 11 feet using the external antenna on top of my baseball cap.
- Color screen - My old GPS has a monochrome screen but my new Garmin has a color screen—boy, what a difference! I recommend getting a color screen if you plan to use a road map database in your GPS (or topographic maps). This lets the GPS use different colors for different types of roads, as well as different types of points of interest. This might not seem like a big deal, but imagine if the paper road maps that you use were all printed in black & white—they would be much more difficult to use.
- Extra memory - Many GPS receivers have extra memory for storing a map database (roads and points of interest, or perhaps marine charts or topographic maps). If you're going to use the map database feature, get a GPS that accepts an external plug-in memory chip rather than using a fixed amount of permanently-installed memory. The plug-in microSD chip on my Garmin is about the size of a fingernail but stores two gigabytes of data. This lets me store the entire North American road map database, with lots of room to spare. The extra memory can be used to store extra-large track logs.
- USB interface - By all means, get a GPS with a USB interface instead of (or in addition to) a serial port, since it's very easy to connect to a PC. You will use the PC interface a lot to download track logs and waypoints to Google Earth, and also to program the memory chip with the road map database (if you use that feature). You still need a serial port if you're going to use the GPS on a boat and need to interface it to another piece of equipment via the NMEA interface.
- Battery type - You can save money by using rechargeable NiMH batteries, but be sure the GPS accepts both battery types (alkaline and NiMH) and configure the GPS for NiMH batteries. Get high-capacity NiMH batteries (for example, 2500 mAh) and a good charger. Avoid cheap fast chargers (for example, a 1-hour charger for $15) since they can overcharge and damage the batteries. I use a Sony charger that works fine (model number BCG-34HE).
- Multipurpose use - If you're going to buy a new GPS, consider all the things you might want to do with it, and buy a GPS that can serve all your needs. For example, I bought a GPS with extra memory and additional features so I could load a road map database and do automatic trip routing while driving my car. My GPS can also load marine charts so I can use it on my boat. If you decide to get these extra accessories, shop around for a package deal that can save you quite a bit over the cost of the accessories priced separately.
- Additional software - The GPS may come with additional software that runs on a PC. If you have a Vista PC, make sure the software is compatible, likewise for the USB drivers that allow the PC to communicate with the GPS. Check the manufacturer's website, since you might be able to upgrade the PC software and even the internal GPS firmware to the most recent version.
- Owner's manual - If available, download the owner's manual to your PC. This makes it easy to browse and search.
Digital Camera
You use the digital camera for two purposes: to take pictures of points of interest that you plan to feature on your trail map, and to take pictures of the trail environment, including its twists and turns. The idea is to capture the "context" of the trail—that is, its relationship to the surrounding terrain. Later on when you create the map using Google Earth, you can refer to the photographs while viewing the Google imagery to get a better idea of where to draw the trail or placemark.
Any type of digital camera will do. It helps to have a zoom lens that goes from moderate wide-angle to moderate telephoto. The camera should have a big enough memory card to store a couple hundred pictures, since if you walk a long and twisty-turny trail, you might wind up taking lots of pictures.
Note-Taking In The Field
While you're walking around capturing GPS data and photographs, you'll need some way to take notes. For example, when you capture waypoints at trail intersections or points of interest, you need to remember the purpose of each waypoint. Also, if you spot new trails or points of interest that you need to revisit, you need to remember that, too. You can also take notes about special trail conditions, locations of fences and gates, information from signs that you come across, etc.
I used a digital voice recorder to take notes, which I found to be very convenient in the field. I used a Sony ICD-SX46, which is very small and easy to use without looking at the buttons (once you get used to it). The sound quality is good enough that I also use it to record bird calls, gurgling streams, peeping frogs, and other sounds of nature, which are fun to listen to back at the computer.
The voice recorder came with a software program that installed on my PC to download the voice files from the recorder to the PC (via a miniature USB connector) as well as to play back the voice files. Each voice file name has a date/time stamp that allows you to correlate the voice notes with the photographs and GPS information, which also have a date/time stamp.
Once I get back to the computer and download the voice files, I play them back and manually transcribe them into a text file. I think it's easier to view a single text file rather than playing back multiple voice comments every time I need to refer to them.
Unfortunately, the voice recorder couldn't be configured for NiMH rechargeable batteries, which is a shame. If you try to use NiMH batteries, the battery readout indicates that the batteries are nearly dead, even if they are freshly charged. This is because NiMH batteries have a lower output voltage than regular alkaline batteries.
Google Earth Plus
If you don't already have this version of Google Earth, go ahead and pay $20 a year to get a license key. It uses the same run-time version of Google Earth, so there's nothing else to download. The Plus version allows you to easily download track logs and waypoints from a GPS right into Google Earth, then the information displays properly on the screen. It's possible to use the free version of Google Earth if you use some other program to download the GPS data and convert it into a kmz file that Google Earth can read (for example, GPS Visualizer).
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