Review of the Garmin GPSMAP-175 by Joe Mehaffey and Jack Yeazel 10 Feb 1997 (GPS Information HOME PAGE = http://gpsinformation.net/main) We received a new GM-175 for test and Jack and I have been comparing it to the G-12XL. The GM-175 is about the size of a brick (19x5.5x7.5cm) and weighs 20 ounces compared to the G-12XL at 9 oz. While bulky, the unit is shaped to comfortably fit your hand while permitting one hand operation. The three shades of grey display makes maps easier to read and is much larger at 2.4 x 3.5inches (6x9cm) as compared to 1.5x2.1inches (3.75x5.5cm) for the G-12XL. The display on the GM-175 has a higher resolu- tion than the G-45XL and G-12XL. This permits finer detail on the map displays. The computed information such as bearing, distance, lon/lat, etc are displayed in font size about twice that of the G-12XL and the display contrast is very good. The general appearance of the GM-175 is similar to the G-12XL expanded in every dimension. The power and data cable connector is NOT similar to that in the lower cost Garmin units. It is more like the Motorola STS Handie-Talkie microphone cable. Unfortunately, it CAN be installed backward and there is no picture of how to install the cable and no indication that you have installed the connector backwards. And.. luckily, (in our case) nothing bad happened except the data output did not work. (You know... Non standard for the sake of being non standard and hard for the casual user to duplicate.) The GM-175 has a "G-chart" plug in map cartridge for local area maps and is the maps are accurate to +/- 160 feet. This small cartridge is sized about 2x4.5cm and is NOT a PCMCIA memory card. The built in map feature will be useful to Mariners, but those who are used to SA4 and similar will be disappointed in the road detail. Only major highways and state roads are shown for the most part. The marine charts by comparison have a good amount of detail. First, a review of features and operation: Note: ** indicates feature very similar to that provided in G-12XL. When you turn the unit on, a lengthy message appears to tell you to use government charts for navigation for safety. The user must then press "enter" to acknowledge this message and start tracking. (There is no way to bypass this message and it gets old very fast.) The GM-175 does lock on to the SV signals quickly. From a "cold" start, after a 600 mile UPS trip, it locked on in 53 seconds. After a half hour off time, the lock up time was 35 seconds. Specifications are the same as the G- 12XL. "Warm start" , 15 seconds, "cold start" 45 seconds, "autolocate" and "sky search", rated 5 minutes. The GM-175 has an "initialize by moving the cursor on the world map to your approximate location feature". This is used when you have traveled far and the unit is taking too long to initialize. **The specification for position accuracy is 100 meters with SA, 15 meters exclusive of SA and 5 meters with suitable DGPS correc- tion signals. (Note: One place in the manual specifies 5 meters with DGPS, another specifies "better than 10 meters with the GBR-21 DGPS receiver". Garmin says the 5 meter figure with the GBR-21 is correct.) The GM-175 does NOT have the G-12XL's waypoint averaging feature. The GM-175 operates from 6 AA batteries or from external power in the range of 6 to 40 volts DC. 10 hours is specified as the battery life for alkaline cells. We have not tested this parame- ter. A slide on battery pack can hold AA cells or a ni-cad rechargeable battery pack. The external antenna connector a miniature coax connector, is located on the left side, top of the unit. The connector is a MCX type available from DigiKey. **The unit puts out a variety of NMEA protocols, 0180, 0182, 0183 ver 1.5, and 0183 ver 2.0. Other proprietary sentences are output as well. DGPS signals in the RTCM-104 format are accepted at four baud rates to 200bd. A setup screen permits selection of the NMEA/RTCM I/O combination needed by a particular application from six possible arrangements. The GM-175 permits the user to down/upload almanac and proximity data as well as the usual routes, tracks, and waypoints. The GM-175 has a number of features and displays that are useful. These include: **a) A tape type compass display screen (the POSITION SCREEN, with larger letters than the G-12XL) shows direction of travel, track bearing, speed over ground, trip distance (odometer), altitude, lon/lat position, and time of day. As with the 12XL, you must set in the time offset from UTC manually. A DC voltage readout may be selected to replace any one of the above display items. b) Unlike the G-12XL, A circular compass type display is NOT provided. However, the same information can be provided on the GM-175's "highway" display **c) A highway page type display screen shows off track distance similar to a CDI display. The CDI off track scale is ad- justable in units of .25, .50, 1, 2 and 4 sm, nm, or km. This screen includes ANY SIX OF bearing, distance to wpt, speed over ground, course over ground, estimated time of arrival, estimated time enroute, crosstrack error, veloc- ity made good, turn angle to waypoint, and course to steer, all with reference to the next waypoint. The name of the next waypoint is also displayed. **d) A moving map display is provided to plot your course over ground. In addition, bearing, distance, track (course) over ground, and speed over ground are provided on this same display. Whenever the cursor is active, a pop up window appears below the data window showing the position, range and bearing to the cursor or a selected waypoint or navaid. In addition, options allow a tape compass dis- play or a CDI scale to appear on the map display. The selected map scale appears at the bottom of the map display. This feature is similar to the map track feature in the G- 12XL, except that actual background maps are provided by the GM-175 itself. Any waypoints saved in the machine are displayed on the moving map page as they come within range of the map scale selected. Note. The "map" is essentially an "outline of the continents of the world" map page until you put in your waypoints and /or G-chart cartridge. This screen has pan and zoom and scales from .2 mile to 2048 (miles or other units) which works quite intuitively. You can use the cursor to "point" at a waypoint on the map and the distance and bearing to that waypoint from your present position will be displayed. You can also "mark" and store a new waypoint by moving the cursor to the desired position on the map and pressing the MARK key plus ENTER. Several other methods are available to mark waypoints, navaids, etc. The map may be north up, or current track up. The user can select which features, such as road, navaids, waypoints, etc. which are to display at various map scales. The map screen also supports zoom and pan features. Note: The G-12XL provides no built in maps. e) A trip and fuel planner menu permits calculation and storage of relevant information. A distance and sun screen (similar to that in the G-12XL) is provided in the "trip and fuel planner" menu to compute the distance between any two way- points and to display sunrise and sunset information for your locality. **f) A simulator feature provides display of simulated motion and simultaneously outputs simulated tracking data to your computer for test of mapping software, data gathering simulations and such. **g) A screen backlighting timer permits setting the backlight to No Timeout, 15, 30, 60, 120, and 240 seconds when the unit is on battery power. Unlike the G-12XL, the screen will NOT stay on continuously if external power is connected and the backlighting is turned on. The backlighting is uniform and tinted a light grey/pink and the display at night is easy to read. The display is clear and appears to be the same resolution as that on the Garmin G-45/G-12XL. Screen contrast is also adjustable on the setup screen. **h) You can turn off the warning tone! A screen permits beep on warning messages, keystrokes and warning messages or NONE. **i) A message screen page allows you to view system warnings and messages. These include such things as approaching way- point, no DGPS position, poor gps coverage, and battery is low. The total number of such advisory messages is twenty one. **j) A satellite status page comes up when you first turn the unit on. It displays a "fuel" or battery gauge showing battery remaining, and a "compass" display of satellite numbers (1>32) in view along with signal strength bars for each satellite potentially in view (up to 12). The signal strength bars are hollow if the GPS has found the SV and is not yet locked and changes to solid black when lock is made to each satellite in turn. Each signal strength bar is marked with the associated satellite number. This display (on the GM-175) also has EPE and DOP displayed. (There seems to be a lot of confusion about the meaning of Garmin's "hollow" and "solid" signal strength bars. See more detail at end of this report.) **k) Up to 250 waypoints may be named with a six character name and an waypoint ICON from a list of 36 can be assigned to identify a waypoint on the map display. **l) A track log is provided. Neither the manual nor the unit indicates the maximum number of log points available in the GM-175 but Garmin says the track log has a total of 2048 points. (G-12XL has 1024 maximum.) Older points discarded after the maximum selected number is reached OR (on the GM-175) the options may be set to stop logging when the track log buffer is full. On both the G-12XL and the GM-175, the user can select "automatic" track log which projects a track based on the last two track points. When the GPS finds you off this track vector by more than 25 meters (adjustable on the GM-175 only), it logs another track log point. By this means, the GPS conserves track points and the log will maintain good track resolution while minimizing track point usage. Alternatively, one can elect to log a track point at intervals from every second to up to every 99 hours as needed by filling in a hhmmss entry in the track log screen. Also on the GM-175 (only), the user may log at distance intervals of from 0.01 to 9.99 miles (or other units). **m) A track back feature provides the ability to steer you backwards along your initial outward course without your having to have entered waypoints manually during your out- ward transit. **n) The GM-175 accepts the RTCM-104 version 2.0 DGPS correction format version. The GPS can control the frequency of suit- ably equipped DGPS receivers when it is set to the RTCM/NONE mode (No NMEA data output.). DGPS beacon frequency and signal strength will display on the GM-175 when DGPS activi- ty is present on the RTCM input in the proper format. **o) External I/O signal modes available are: NMEA/NMEA, RTCM/NMEA, and RTCM/NONE. The GM-175 adds NMEA/NONE and NONE/NMEA and DELETES GARM/GARM. HOWEVER, the "Data Transfer" mode seems to work the same as GARM/GARM with the programs we tried. Alert messages alarm DGPS signal failure when that mode is enabled. **p) A waypoint proximity alarm can be programmed to alert the user with an audible "bong" when the selected waypoint is being approached. **q) The user may select a Magnetic heading reference or true north as required. Other options are grid reference and User selectable. **r) The GM-175 has 119 (versus 107 for the G-12XL) built in map datums plus the capability for users to set in their own datum settings. **s) The user may enter his own grid format if desired. The reviewer's opinion is that the GM-175 has a very similar unit feature set and accuracy as compared to the G-12XL EXCEPT for the additional features in the GM-175 to support the internal map system. The map data cartridges cost about $130 for inland maps each requiring (for instance) two for Georgia and three for Texas. Offshore maps are a bit more reasonable at $89 to $349 depending on resolution. For LAND use, the reviewers prefer a laptop computer and something like SA4, VISTA, or MapExpert. For Marine use, the "all in one sealed box" feature may well outweigh any problem of lack of detail. Subjective Observations of Performance Jack Yeazel and I have been out testing the GM-175 and comparing it with the G-12XL in tracking performance including RF sensitivity. We uploaded and downloaded waypoints, tracks and routes using Waypoint+(W95), and G7to..(W3.1). We tried it out on SA4 and Delorme MapExpert, and Vista. No problems found. We compared it with the G-12XL for lock times and the ability to hold lock under various situations. Once lock was acquired, we could find essentially no performance difference between the two units. We found, however, that the G-12XL could routinely maintain lock inside many buildings when the GM-175 would not. The difference was not great, but it was demonstrable. We tried the GM-175 and the G-12XL (both barefoot [antenna wise]) on the dash of our car. We found that the two units had very comparable performance but our G-12XL had a bit more RF sensitiv- ity and would often show one more satellite than the GM-175. This surprised us as reportedly the two units have Garmin's 12 channel parallel receiver. Perhaps one year of technology development has benefited the G-12XL and has not yet been applied to the older GM-175 or perhaps we are seeing sample differences. We were impressed at the speed that the GM-175 and the G-12XL respond to changes in direction as compared to the older G-45 and the M-4000. At about 4mph, the GM-175 and the G-12xl would complete a change of direction in about 15 feet, the G-45 about 50ft, and the M-4000, about 60ft. Both the GM-175 and the G- 12XL laid down smooth tracks on our highway maps during all tests. However, we noted that there were occasional minor jumps in tracks on the order of 100 feet with the GM-175. While both units have a "dead reckoning" feature when tracking is lost, The GM-175 apparently has less data smoothing. This is probably not a bad feature where the instrument is to be used with marine autopilots which also may implement data smoothing. Garmin told us that the GM-175 uses adjustable filters for data smoothing whereas the G-12XL filters are fixed. With the GM-175, the velocity/track data filter may be ON, AUTO, or OFF. OFF gives instantaneous readings unfiltered which will jump around with SA, etc. This is suitable for autopilots which have built in filtering and which might be unstable if additional filtering is added in the control loop. ON gives a continuous high damping of both track and velocity measurements. This is supposedly designed for use on slow moving boats such as sailboats. AUTO will constantly adjust the filter's time constant based on track and speed and rates of change of track and speed. These are the major features and operational differences we have observed in a couple of days of working with the GM-175 and comparing the G-12XL. Our initial impressions are that the GM- 175 is an impressively equipped GPS instrument with a capable built in mapping feature. The satellite acquisition is fast but in identical low signal situations inside buildings, the G-12XL routinely outperformed the GM-175 in acquiring SVs. (We wonder when someone will put a mini-CDROM in a mapping unit so we landlubbers can have a really good map at reasonable cost in a stand alone GPS mapping unit.) There are a large number of additional navigation feature in the GM-175 as compared to lower cost units. The extensive mapping and marine navigation features will appeal to many. The more frequently used items are easy to use, but the more obscure may require several screens and menus and half a dozen button pushes to access. All in all, We like the GM-175 and feel that it is a rugged, competent unit. We thank CommSystems Intermountain/Salt Lake City for the loan of the GM-175 used in this evaluation. If anyone has any additions, questions, or comments, please feel free to Email Jack or Joe. Joe Mehaffey and Jack Yeazel joe@mehaffey.us JAck@FinalApproach.net