G38 vs. the GIII Pilot

This is an old message that was posted to sci.geo.satellite-nav on 11/05/1997. The idea was to compare the lowest unit from Garmin to the highest unit from Garmin at the time. Of course the GIII pilot wins but you may still find it useful since it describes the GIII pilot.

I recently got a chance to play with a GPSIII Pilot, hereafter called a 3P, and I own a GPS38, called a 38. In this article I will attempt to give you my impressions of the 3P and compare it to my older 38. This is only a first impression with less than a week on the 3P but I have to give it back so a first impression is all I have. Of course the two units are vastly different but I'll do the best I can to compare them.

Configuration 38 - software 3.04. 3P software 2.00 The 38 is a single channel unit that can track 8 satellites. The user interface is similar to all handheld garmins before the III series. The 3P is a twelve parallel unit that has built in maps. It is the Pilot version of the III that has already been discussed in this group.

The test condition was a hike in open terrain of about 5 miles round trip. The return retraced the outbound route. Of course a Pilot unit is designed for airplanes but I still think the comparison on a hike is OK. At least I can stop and compare things without crashing! I am not a pilot so the 3P features may not be fully appreciated by me but since there hasn't been much posted about them I figure some data is better than none.

First I powered them up. The 3P has two warning screens that must be answered everytime you power up. TWO, surely one would have been enough. You can immediately enter the simulator mode by hitting the menu key and selecting Simulator. You will then get another warning screen telling you not to use the simulator for navigation. Are pilots really this stupid? 3 warnings and I haven't done anything yet. My 38 has no warnings that I have to answer which is fine by me.

(By the way, while we are talking about powering on the unit. There are two undocumented ways to power up a 3P and three for a 38. Holding down the enter key on either unit while powering up will causing a test mode to be entered that can be used to test the keys and displays. Don't use this mode where satellites can be acquired since Garmin warns that this messes up some temperature tracking data temporarily. Holding down the mark key (menu key on the 3P) and powering up will erase everything!!! Yes--all user data, no warning on either unit. Note that the mark key on the 38 and the menu key on the 3P are in the same relative keyboard position. On the 3P this will reset the clock that says only reset at the factory. From information in this group the GPSIII (non pilot) may use different keys for this. On the 38 you can power up and then hit the four arrow keys in succession to bring up a diagnostic mode. This adds some data to the screens. Most of the valuable user data from this mode is already present in the 3P anyway.)

Before we get into the actual comparison I will digress again and talk a little about the 3P. There is very little data on this unit available and it is different from the GPSIII in several ways based on what I have heard about the III in this group. For example the track log is different. There are no separate compressed track logs, just one, like the 38. I don't know how long the track log is because there is nothing in the manual or the garmin web site about the length and the data is expressed as a percentage. There are features built into the unit to do vertical navigation where you define the climb rate capabilities of your plane and the unit will help you to get to the correct altitude and warn you when you move too far away. There are also special calculations available where you can feed the data from the gauges on the plane into the unit and compare the airplane information to the GPS ground information. These differences can be used, for example, to calculate wind speed and direction, which is useful data to predict fuel consumption. These are just a sampling of the differences.

It is always said that the difference between the 3 and the 3P is the jeppesen database but what does this mean? Well at first glance it would appear that there is this database in the unit that you can use to look things up in, much like a similar database that you can get for an HP calculator. And this is indeed the case, but there is a lot more. The database is integrated into the other functions of the unit and expand the capabilities accordingly. For example when getting the nearest waypoints you can specify that you want the nearest airports, or the nearest VORs, or the nearest user waypoints (like the 38), or the nearest ... There are many things you can get. The map display will automatically include waypoints from the jeppesen database as well as the ones you define. The map display also can include the air control areas plotted over the top of the map and will alert you when you pass from one control space to another if you wish. While user waypoints still don't save the altitude the jeppesen database of waypoints includes altitude and can be used as part of the vertical navigation feature described above. You can control the level of detail on the map display for jeppesen data or turn it off entirely. You can have jeppesen data and not ground mapping data, or you can reduce the contrast of the ground mapping data so that it seems to be in the background. You can use the map to measure distance to jeppesen or user defined waypoints. You select it graphically but the display is numeric and dynamically updated. The jeppesen data seems to be worldwide even though the maps aren't.

The big deal in the III and the 3P are the maps. They are worldwide down to a level of 50 miles scale and include political boundaries and major cities. The Americas version I had then includes more detailed road maps of the western hemisphere. You can control the level of detail based on the zoom level. You can set up messages in the 3P that alert you when you cross a political boundary. There is a grid system that you can turn on which replaces the circles in the 38 map. There is a bread crumb track log which is pretty faint and not as noticeable as the one on the 38. On the 38 you can specify how many points from the track log are displayed on the map. I found no corresponding feature in the 3P. The 3P has icons, of course, as do many of garmins newer units. I was unable to change the default icons even though the manual says I should be able to. Seems like a bug. I couldn't get the icon to highlight in the waypoint display. The default track icon is a pair of feet which is terrible since it is two objects and at various zoom factors it became impossible to tell how many icons you were seeing. One icon should be one object. The 38 has no icons.

Update: I finally was able to highlight and change the default icons for user waypoints. If you move the cursor down the screen the icon is skipped but if you move the cursor up the screen then the icon becomes selected and you can change. Definately a bug.

Now for the live comparison. The 3P will lock on satellites through the roof of my house! It won't lock through two floors but it is amazing. In open terrain it reports more satellites available than the 38. (The ones near the horizon) and will track the same or sometimes one or two more. It locks a lot faster and maintains the locks better as would be expected. It seems to respond much faster to everything which is sometimes not so good. Altitude, for example, varies much faster than the 38 but is no more accurate it seems. In general the positions seem to agree down to the last digit in lat/lon on the display. (That is the least significant digit would vary by 4 or 5.) Interestingly the clock on the 3P was about 12 seconds ahead of the 38 at all times. Having the faster response meant that the map display needs to be set for North up since otherwise if you set track up the SA causes the maps to jump around too much while hiking or stopped.

The satellite page would usually indicate a better epe for the 3P but the dop and fom comparison did not always correspond with the 38 sometimes say better and sometimes worse. (DOP is 3P and FOM is 38 with an undocumented startup.) The next next navigation screen was roughly the same for the two units. The 3P allows you to customize 6 things to watch while the 38 is fixed. The 3P will also tell you the date. For some reason the 3P indicated that I traveled slightly less on the trip than the 38 said. And as mentioned before the 3P data would vary more rapidly making comparison difficult. SA affected both units, usually the same but sometimes differently, probably because of the extra satellites the 3P would show from time to time. Compass drift was the most noticeable difference although walking speed varied quite a bit between the two units as did altitude. The lat/lon fix varied the least of the data I checked. The 3P data was more readable with the higher resolution display.

The map screens were quite a bit alike at this level of use. (The built in map is unusable for hiking a trail so you just zoom in and use it like you would without a map.) The 3P lets you customize the 4 data objects you wish to display while the 38 does not. The airplane icon indicating your present position would rotate based on the heading which was a nice feature. You could tell readily when the unit picked up on the fact that you changed directions. Generally the 3P seemed to track direction changes a bit faster than the 38 but not very much faster. The zoom scale numbers do not correspond between the two units. The dedicated zoom keys on the 3P were nice. Moving the cursor over an object on the 3P highlights the object name and you can hit enter for more detailed info on the object. This is nice for waypoints.

The next screen is the compass navigation screen on both units. The 3P compass screen (called HSI) is much better than the 38. The compass rose has detailed compass headings and is more usable than the 38. You can customize the data you wish to see and cross track data can be zoomed if you wish to change the scale.

On the 38 you switch to the highway screen with enter from the compass screen. On the 3P it is just the next screen in the rotation. For hiking use the 38 has a better highway screen than the 3P IMHO. It contains 8 pieces of useful information compared to the 3P's 5 pieces. Both have the ability to customize the data you see. The 3P data is a bit more readable based on the higher resolution display but for hiking this is not an issue. The 3P can zoom the highway display but this isn't particularly useful. The 38 would tell you how to steer if you go too far off track but the 3P would not. Because of rapid compass variation described above the 3P would often show a different direction than the 38. Not more accurate or less accurate just different.

The 3P would always switch through a route screen while the 38 would skip display of this screen unless a route was active. It seemed to be a little easier to find setups on the 38 but this is probably just because I know it better. There was data available from the menu screen on the 38 that provided information, for example sunrise and sunset. On the 3P you would need to pick one of your regular screens and convert the displayed information to get this data then you would have to convert it back. This is less useful to view data you only reference occasionally. The 3P has collects more data, such and max speed and two odometers, that can be displayed. Battery voltage is only available on the 38 using an undocumented startup but is available on the 3P by customizing one of your screen displays to see it. I would have really liked to see a menu item that just let me scroll through all of this extra data and view it without having to mess with one of my regular screens.

One of the interesting features in the 3P is the ability to switch screens from horizontal to vertical orientation. (Hold down the page key for a second and it will switch.) What isn't documented is the fact that the two displays are separately customizable. This means you can re-order the information in the two displays or even display different things! So if you have a preferred orientation and are willing to crane your neck a little then you can set up a main display in your normal orientation and set up completely different secondary data in the switched display. With the more than 30 different things to display in the 3P (as compared to about a dozen in the 38) this can be really helpful.

Both the 38 and the 3P will actually replay a route in the simulation mode. They will go to the trackpoints and automatically make the turns. At slow speeds they look much the same but the 38 won't play back faster than 99 units just like in normal mode. The 3P will go up to 999 units and when you go fast it assumes you must be flying! For this reason it rounds out the turns like an airplane would and it will even give you a warning about a steep banking turn if the corner is too abrupt. Both units output data to a computer and the computer can't tell whether the data is coming live or from simulation mode so you can replay a track to a remote moving map display if you wish. Speed is entered on the 38 by just selecting the speed display and changing it. Similarly for the heading. On the 3P this cannot be done on the position page but from the compass or highway pages the Up and down arrow keys change the speed by 10 units while the left and right keys change the heading. To get an absolute setting on the speed or heading you would need to bring up a menu. On the 38 you can also set the lat/lon the same as you can set the speed or heading. This is not available on the 3P.

Both units let you enter waypoints directly on the map display but, of course, having the real map underneath the 3P make figuring out where to set the points a bit easier. The 3P will even let you build a route this way. This brings up the second bug in the 3P. You can pan and just hit enter to create a waypoint (mark on the 38) and the 3P will bring up a form that you can use to change the name, description. But if you decide you don't want the waypoint you might try and hit quit. Unfortunately this will not cancel the waypoint. It will be created anyway.

Both units will let you select a displayed waypoint on the map and view the data about the waypoint. The 3P will let you view the map from the waypoint list data as well.

The 38 has a MOB feature to set a waypoint at the current location and automatically set the goto information to this waypoint. There is no MOB function on the 3P. Otherwise the goto functions on the two units behave similarly. The 3P places the goto destination on the route page.

The 3P eats batteries at twice the rate of my 38. Both have external power connectors although the 38 is limited to a 5-8 volt input while the 3P will use 10-32 Volts. Both can work with a DGPS input but the programmability of the interface is more limited on the 3P for input and output.

Neither unit has an audible alarm but both units attempt a visual alarm. This is done by bringing up a message box and turning on the light at night. The 38 only has an alarm for getting close (within a minute) of a targeted waypoint. The 3P has lots of alarms and they are programmable. You can turn them off or set their sensitivity. There is a timer alarm, waypoint proximity, air space proximity, etc.

The 3P has a trip planning feature that you can set the expected speed and fuel consumption for the trip. You can review this information during the trip to check your assumptions.

The 3P has a variable output on the lamp and the keys are also lit. The 38 has only the display lighted at a single lamp level. Both units let you program the time delay for the lamp shutting itself off to conserve batteries.

I think I forgot to mention that the compass page on the 3P has two modes. The main one I described yesterday and a second one that displays large characters for your two favorite pieces of information and a small compass.

All in all, a 12 channel unit is the way to go. Now is a III or a II+ your cup of tea? I still haven't decided. The maps are nice, however .... Since I have to give the 3P back I may not be able to answer your questions but as long as you trust my memory, ask away.

Dale DePriest