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GPS Receiver Recommendations

I've had hands-on experience using Tru-Traffic with a few different types of GPS receivers, and they're not equal. The short advice is to get one that uses both of the following

If your GPS receiver has a serial (RS-232) cable but your computer has only a USB port, you can still use a USB-to-serial adaptor to plug it into a USB port. These adaptors come with software drivers for serial port emulation.

Garmin has some GPS receivers (e.g., the eTrex Legend C, Legend Cx, Vista C, Vista Cx, etc.) with USB cable and a purely USB interface — no serial emulation available. These require additional software to work with Tru-Traffic. One software product, Franson's GpsGate allows GPS-enabled applications that accept NMEA input over a serial port (for example, Tru-Traffic) to work with Garmin USB-based GPS receivers (using the Garmin USB protocol) by emulating a virtual serial port. It looks like it costs about US$10/computer. A Tru-Traffic user has confirmed that it works fine with the software in NMEA mode. Unfortunately, as far as he can tell, it does not emulate the serial port with the Garmin (proprietary) protocol. This means you can connect the GPS to the laptop out in the field and run just fine, but you cannot, as far as we can tell, take the GPS solo out in the field, use it to record intersection coordinates ("waypoints") and trip logs ("tracks"), then download to the computer when you return to the office.

Chip Sets

Two chips sets seem especially promising for use in urban canyons and under tree canopies: the SiRFstarIII and SiRFstarIIe/LP, which uses SiRFXTrac. A number of manufacturers offer GPS receivers based on these chip sets, including Garmin, HAiCOM, Holux, Magellan, TomTom, and USGlobalsat. If you search for SiRFstarIII, you should get a number of hits. I have personal experience with the HAiCOM, and some USGlobalsats (see below), but not with the rest of these.

GPS Receiver vs. GPS Navigation System

We must distinguish a humble GPS Receiver from full fledged GPS Navigation System, the sort of device you'd put in your car to find addresses and give you driving directions. Most simple GPS Receivers will provide "raw" geographic position & time information, either to a file or, better, over a live connection (a serial port, a Bluetooth connection, a USB port, etc.), which Tru-Traffic needs for its trip analysis. Most of the full fledged GPS Navigation System do not provide "raw" geographic position & time information, providing instead travel routes and driving directions, as they're intended for strictly navigational purposes. As such, most GPS Navigation System are not suitable for use with Tru-Traffic for travel time & delay studies. If the specifications for your device mention NMEA 0183 somewhere, then it will almost certainly work with Tru-Traffic for travel time & delay studies. If it does not mention NMEA 0183, then it may or may not work with Tru-Traffic, and you'll need to investigate further to decide which is the case.

Despite my limited experience, I get the impression that anymore, it's hard to go wrong as long as the GPS receiver specifies NMEA 0183 somewhere. If you have experience with any of these units and can offer feedback that may benefit others, please let me know, and I'll post it here.

Recording a Trip Log using the GPS Receiver solo vs. Tru-Traffic

Some GPS receivers double as GPS data loggers; they can record their own trip logs ("tracks"), which gives you options:

  1. You can take the GPS receiver in the field solo, let it record the trip logs, then import the trip logs into Tru-Traffic when you return to the office. For Garmin GPS receivers connected with a serial cable, you can download directly into Tru-Traffic; otherwise, you can use software that comes with the GPS receiver or that's freely available to save the trip logs to a file for importing into Tru-Traffic. Advantages of this include
  2. You can connect the GPS receiver to a laptop running Tru-Traffic, and let the software record the trip logs for you. With the basic GPS receivers that don't have a recording feature, this is your only option. Advantages of this include

The figure below, taken from the User's Manual illustrates the penalty in the speed accuracy that you can incur using option #1, if your GPS receiver doesn't include the speed in its self-recorded trip logs. The associated discussion in the user's manual describes the cause and consequences in more detail. As of this writing, the figure is on page 54 in the user's manual.

Noise in calculated GPS speed.

DeLorme

I've used the original Earthmate (which had only a RS-232 serial connection). This worked well and had the additional advantage that it gave an update every second, as opposed to every 2 seconds as all the NMEA GPS receiver I've tried. It was relatively inexpensive and came with its own mapping software. Disadvantages are that it could work only when connected to a computer, not as a standalone unit, and its battery life was very short, making the power cable connector a virtual necessity. Have you noticed I've been using the past tense here? A perhaps bigger disadvantage is that it's no longer available except through eBay (probably used). I give it a qualified recommendation.

DeLorme has replaced the old Earthmate with a new one, the Earthmate® GPS LT-20 (and GPS LT-40), which has a USB connection and is NMEA-0183 compliant. This new one does work as a standalone unit and is supposed to have a longer battery life. Although the new one does not have an RS-232 serial interface, one can download "COM Port Emulation Drivers for the USB Earthmate GPS Receiver" from the DeLorme web site. Unfortunately these drivers work only on 32-bit (not 64-bit) versions of Windows prior to Window 7, so if you run a 64-bit version of Windows or Windows 7 or above, then you'll need to use the Bluetooth interface to connect to DeLorme's GPS receivers. I've confirmed that these drivers allow the Earthmate to operate with Tru-Traffic, but starting with version 6.0.0.42. At the time of this writing, there's a bug in their NMEA-0183 compliance, and ver. 6.0.0.42 works around this bug. If your computer doesn't have a USB port, DeLorme also sells a serial interface cable.

While my basic testing with the DeLorme Earthmate® GPS LT-20 shows that it works with Tru-Traffic, a user in Houston has used it much more extensively and reports reliability problems when recording trip logs – frequent bad readings and signal interruption messages from Tru-Traffic.

I've been quite happy with DeLorme's Blue Logger, since the wireless setup is so simple. And with Windows 7 changing the rules for USB drivers, Bluetooth is often the only option for using DeLorme's GPS receivers. Cheryl Allen-Munley, of Greenman-Pedersen, Lebanon, NJ contributed detailed instructions on how to get the DeLorme Earthmate GPS BT-20, the successor to the Blue Logger, working with Tru-Traffic running on Windows 7. Thank you, Cheryl!

Deluo

One user has reported being quite happy using the Deluo USB GPS for Laptop with Tru-Traffic. Costing about $55, it's one of the least expensive ones you can buy and supports NMEA through the USB port, so it takes its power from your laptop. Unfortunately, the Deluo USB GPS for Laptop specifications do not indicate that it's using a chipset such as the SiRFstarIII and SiRFstarIIe/LP, which use SiRFXTrac. This isn't critical, and it may not even matter, but without such a chipset, it's likely to have difficulty maintaining a fix in low-signal conditions, such as urban canyons or under tree canopies.

Garmin

Due to design change in recent years, I have to qualify the recommendation for Garmin GPS devices. Some of them work fine as GPS data loggers, and some work also connected (through Franson's GpsGate) directly to Tru-Traffic for monitoring "here" and "now" in your arterial timings diagrams, but some of the recent models are unsuitable for either purpose, and I can no longer keep track of which ones serve us well and which ones don't. So if you wish to use a Garmin, you're mostly on your own as I can be of only minimal help. A GPSBabel web page monitors the capabilities of the various Garmins, including the current ones.

I've tried 4 different Garmin GPS receivers,

  1. the GPSmap 60,
  2. the basic eTrex,
  3. the eTrex Legend (that is, just "Legend", not the newer, USB-based "Legend C" or "Legend Cx"), and
  4. an older model (so old, I couldn't even find a model number).

They all worked fairly well with Tru-Traffic. The basic eTrex is relatively inexpensive (but requires separate purchase of the data cable), and they all have the advantages that they have a fairly long battery life and can also work as a standalone unit — they don't have to be connected to the laptop. I give them a qualified recommendation. I have to qualify it because a number of users, including me, have encountered these bouts where the software and the GPS receiver suddenly stop communicating altogether for no obvious reason -- the Diagnostics page just stops scrolling. None of us know what's the pattern. Usually, when this happens, we can break it loose from whatever stupor it's in by restarting the GPS receiver and/or the software. Often toggling the communications protocol (from Garmin to NMEA 0183, or from NMEA 0183 to Garmin) in both the GPS receiver and the software does the trick. Sometimes we have to reboot. Eventually, it all starts to work again, and it's generally pretty reliable, but this is enough of a nuisance that I have to qualify my recommendation. The Pharos receivers (the one that used to come with Microsoft Streets & Trips with GPS Locator) and the DeLorme Blue Logger both seem more dependable with the software to me.

In comparing Garmin GPS receivers, it is important to distinguish the ones that have only a USB interface from those that have serial (or both serial and USB) or Bluetooth interface. Check the specification page for the GPS receiver before buying to determing which type of interface(s) it has. For maximum flexibility in working with Tru-Traffic, choose a GPS receiver with serial (or both serial and USB) or Bluetooth interface, not one with a USB-only interface. Be aware that with many of the GPS receivers that support both serial and USB, getting the serial cable requires a separate purchase. You should do this (buy the optional serial cable if it's not included) for maximum flexibility in working with Tru-Traffic, as downloading pre-recorded trip logs directly to Tru-Traffic requires connecting the GPS receiver via its serial cable. The serial cable may be connected to a USB-to-serial adaptor, if necessary, to plug into your computer's USB port, but the connection on the GPS receiver side still must be with the serial cable, not the USB cable, if you want to download pre-recorded trip logs directly to Tru-Traffic.

If you get a USB-only Garmin GPS receiver, or you don't have the serial cable, then at present you must use some additional software to either connect the GPS receiver to Tru-Traffic or to download the pre-recorded trip logs to a file for importing into Tru-Traffic. You may use the software product Franson's GpsGate to emulate a virtual serial port so you can connect the GPS receiver to Tru-Traffic. See the discussion of that software above for more details. One user reports successfully using DeLorme Serial Emulator for this purpose. Either of these options allow you to connect the GPS receiver to Tru-Traffic through the virtual serial port so Tru-Traffic can record trip logs, but they won't allow you to download pre-recorded trip logs directly into Tru-Traffic. To download pre-recorded trip logs, you may use

  1. Garmin's MapSource
  2. GPSBabel
  3. GPS Utility, or
  4. EasyGPS

to download trips and save them in, say, a .GPX file for subsequent importing into Tru-Traffic. A FAQ gives some additional details.

Starting with version 6.0, Tru-Traffic includes additional support for Garmin GPS receivers. You can use the Garmin proprietary interface, instead of the NMEA interface, provided you have either a serial port or a virtual serial port. An advantage here is that in the Garmin proprietary mode, the GPS receiver gives an update every second, as opposed to every 2 seconds. Also, you can download pre-recorded trip logs from the Garmin GPS receiver. This allows you to take just the GPS receiver out in the field, without the laptop, record you trips, then download them into Tru-Traffic after you return to the office.

HAiCOM

These seem to work nicely. One I've used, the
HAiCOM HI-303S CompactFlash CF GPS w/ SiRF Xtrac v2
is designed to work in urban areas or where the signal is weak. The "SiRF Xtrac v2" is significant because they offer another HAiCOM HI-303S GPS that includes WAAS support (for improved accuracy) instead of SiRF Xtrac v2 (for urban areas). I've confirmed that the SiRF Xtrac v2 model is basically compatible with the software, but I don't have a sufficiently stressful environment to test whether it offers adequate, or even improved, performance over other receivers in urban canyons or areas with lots of noise. I'm hoping to hear feedback from Tru-Traffic users about its performance. A user in Las Vegas (which we believe has interference problems along the Strip) has borrowed my receiver for testing there, and I hope Salt Lake City and Houston (both of which have reported GPS problems within certain regions of their cities, possibly due to effects of urban canyons) will also test it eventually. If you all decide to test this GPS receiver, I would be most eager to hear your report.

Magellan

I've personally used only the Magellan GPS 315 receiver, an older model. This worked fairly well, but not quite well enough that I can recommend it without reservation. I found that it fairly frequently stopped reporting a current, tracked, position for long intervals — 10 seconds or more. While recording trip logs, Tru-Traffic doesn't like these long gaps. I tested this with a Garmin eTrex Legend, each connected to a (different) laptop simultaneously running Tru-Traffic and both sitting side by side on my dash board. I had many more problematic gaps with the Magellan than I did with the Garmin. I'm not sure if the Magellan GPS receiver just lost the satellite signals more easily than the Garmin, or if both lost satellites but the Garmin recovered more quickly, or if the Garmin was just dead reckoning — extrapolating from the last reliable reading — as Garmins do. Probably the latter. But either way, I had many more troublesome gaps with the Magellan.

I don't know if these problems persist with more current models, but the experience of some Tru-Traffic users in North Carolina does not sound promising. They're using Magellan Meridians (newer than the receiver I used, but older than the ones available now, 4/24/03), and have reported similar problems. We haven't confirmed that the problems are identical to the ones I had, but everything we could compare sounded perfectly consistent. Right now, I'd recommend using a Magellan only if you have one already. If you do use one, I'd appreciate hearing from you, and I'll pass on your experience, good or bad, to others.

Trimble

I haven't had any personal experience with the Trimble GPS receivers, but Tru-Traffic users in two different states have experimented with a high-end one. Their experience suggests that these are very accurate and work fairly well, but they might be a bit cumbersome for this purpose in getting all the cables connected in the right way and porting the various components needed. Also, they report that compared to a Magellan Meridian, their Trimble seems to be a bit picky — quick to lose a fix when the satellite signal becomes weak, and slow to recover a fix when the signal is restored. Their impression is that the Trimble insists on a high degree of accuracy, and when it can't deliver that accuracy, it's silent. One set of users' tests suggest that the Magellan works fine in all the Trimble's dead spots around the city. They prefer the Magellan over the Trimble.

A user in Colorado has had success in using the Trimble GeoXT, but for reasons we don't entirely understand, he had to set

Using the NMEA/4800 mode seemed to be unreliable.

A user in California experimented with the Trimble Lassen-iQ GPS receiver. It seems that the reports from the GPS receiver omit the $GPRMC sentence. Tru-Traffic prefers this sentence because it includes the date (as well as the speed and heading). Instead, the GPS receiver reports the $GPVTG sentence, which gives speed, but does not give date or heading. Tru-Traffic displays a Searching for Fix message until it has a set of reports that include position, date, and time. This GPS receiver also omits pretty much all information about the satellites, but Tru-Traffic doesn't really use that information except to display to the user for help in diagnoses.

I could modify Tru-Traffic to accept the $GPVTG sentence, supply the date from the computer's clock, and substitue a calculated heading from consecutive positions, but this is not a great compromise, as computer clocks become notoriously unreliable as the batteries wear down, and calculated headings are much less reliable at slow speeds or at a stop. For the time being, I recommend choosing a different GPS receiver, one that includes the $GPRMC sentence in its reports.

USGlobalsat

Three different users (including one here) have reported great results with the Globalsat BU-353 Cable GPS receiver. It has some appealing features. It includes a magnetic mount, a waterproof casing, and a 5-ft USB cable so you can easily mount it on the roof of a vehicle with good exposure to the sky. It uses the SiRF Star III GPS chipset and an active patch antenna for high accuracy and sensitivity.

For the convenience of Tru-Traffic Software customers who want one-stop shopping or a simplified selection of suitable GPS devices, the Tru-Traffic Order Form offers this basic GPS receiver and several of the GPS Receiver+Data Loggers from USGlobalsat. These GPS Data Loggers may be configured to record speed, so they can avoid the problem described above. You can find them available at lower prices online. They're on the Tru-Traffic Order Form merely as a convenience.

Other

There are GPS receivers from other manufacturers, but I have no personal experience with them, and I don't know of any Tru-Traffic users working with them, so right now I can't pass on any more information about them.