Lowrance iFinder Pro and Garmin GPSMAP 76C Product Review

Users of Global Positioning System (GPS) technology for natural resources management purposes collect geographic data in one of three forms: single geographic points, and collections of points in the form of either lines or polygons. In GPS terminology, point data is collected as waypoints, and linear and polygonal data are collected as tracks or trails (two names for the same thing). For these uses, the two most important features of the GPS receiver is a large onboard memory in which to store the maximum number of geographic points, and the ability to move the collected data to a computer for use with mapping software.

Although the basic Garmin eTrex remains the simplest, easiest-to-use, and least expensive GPS receiver on the market, and is certainly adequate for these natural resources uses, its onboard memory is limited, and a number of BIA users have indicated a preference for a unit which supports the display of maps in real time. At the same time, limited budgets and the need for simplicity rules out the most expensive and complex receivers favored by surveyors and Geographic Information System (GIS) professionals. Two new receivers - the Garmin GPSMAP 76C and the Lowrance iFinder Pro - offer a combination of features that fulfill the requirements of large onboard memory, map display, simplicity, and low cost.

Side-by-Side Comparison

Lowrance iFinder Pro+	Garmin GPSMAP 76C

Cost: Manufacturer's Suggested Retail - $299 (with the "+" package, which is strongly recommended as it comes with the MMC/SD card reader, and 16 Meg MMC card which are needed to interface with the computer. Also comes with the "Map Create" software for installing detailed maps into the iFinder.) Lowest price on the Web as of 10/18/04 - $269.00	Manufacture's Suggested Retail - $499 (Includes USB interface cable and MapSource Trip and Waypoint Manager Software.) comes with the MMC/SD card reader, and 16 Meg MMC card which are needed to interface with the computer. Also comes with the "Map Create" software for installing detailed maps into the iFinder.) Lowest Price on the Web as of 10/18/04 - $395 less $50 Rebate

Map Display: Proprietary "Map Create" Products. Topographical maps are available. Did not test map products.	Proprietary "Map Source" Products. Topographical maps are available. are available. Did not test map products.

Memory: Actual onboard memory size is unspecified, but through the simple device of an onboard MMC/SD slot, Lowrance has made the memory capacity of the iFinder virtually unlimited. The slot will accept an MMC/SD card of up to 512 Megabytes, and as onboard memory is exhausted, waypoint and trail data can be transferred to the card and onboard memory refreshed. Waypoints: 1,000 in onboard memory Trails: Lowrance specifications call for 99 savable trails, with "up to 9,999 points per trail". This takes some interpretation, as it does NOT mean that the iFinder will hold just under a million points (99 x 9,999). It will save 99 separate and distinct trails, and each trail will save up to 9,999 points, but the onboard memory is limited to about 55,000 separate points in waypoints and trails combined. If trails are loaded to the maximum of 9,999 points, then the onboard memory is exhausted about halfway through the sixth trail. With an MMC/SD card installed, however, this is a moot issue, as the five full trails can be copied as a file to the card, the trails in memory deleted, and cycle started over. A 512 Meg MMC/SD card will hold several thousand trails, and a pocket will hold several MMC/SD cards. For practical purposes, capacity is infinite.	Actual onboard memory is listed as 115 Megabytes, most of which is dedicated to storing "Map Source" maps. onboard MMC/SD slot, Lowrance has made the memory capacity of the iFinder virtually unlimited.board memory is exhausted, waypoint and trail data can be transferred to the card and onboard memory refreshed. 1,000 in onboard memory. The 76C has a separate category of waypoint called "Geocache" in which enthusiasts of this sport may log their finds. The geocache waypoints are part of the 1,000 waypoint limit. Tracks: 1 Active Track of up to 10,000 points; 20 Saved Tracks of up to 500 points each. Garmin has approached the problem of reducing the Active Track points to 500 differently than in the Model III+ and the eTrex models. In the 76C, if the Active Track has 500 points or less in it, all of the points are saved to the Saved Track. If there are more than 500 points in the Active Track, the number of points is reduced to 500 by an algorithm that examines the track for curvature, saving more points in the curves and fewer points in the straightaways.

Simplicity: (a very subjective analysis): On a scale of 1 - 10, with the basic eTrex being the 1 and the expensive, high-end professional receivers being the 10, the iFinder is about a 5. It is more difficult to use than the 76C and its menus less intuitive. Documentation is better than earlier Lowrance models, although indexing is incomplete. These are common traits of all the Lowrance GPS receivers, and for that reason they are better tools for the experienced, constant user.	On the same scale of 1 - 10, the 76C is no more complex than a 3. Most subordinate menus, including all the setup menus, are listed on the same "page" (receiver screen) and are easy to find. Documentation is not as good as it could be, especially in the indexing, but is readable and presented in a step-by-step fashion.

Specifications from the manufacturer.	Specifications from the manufacturer.

Other Features

Lowrance iFinder Pro+	Garmin GPSMAP 76C

WAAS: Yes; WAAS is hardwired to enabled, and may not be disabled.	Yes; WAAS may be enabled or disabled at will. (There is a slight power savings when WAAS is disabled.)

External Antenna: Yes; iFinder will accept either an active (amplified) or passive external antenna. Same antenna port as the Garmin (will wonders never cease!). iFinder will auto-detect an active antenna, but a passive antenna must be selected in the first menu. A high-gain active antenna will approximately double the signal strength to the receiver.	Yes; The 76C will accept either an active (amplified) or passive external antenna. Same antenna port as the Lowrance and will auto-detect either an active or passive antenna. A high-gain active antenna will approximately double the signal strength to the receiver.

Computer Interface: For downloading waypoints and tracks, the iFinder relies on its MMC/SD card, and it is a very simple system. With the data copied to the card, place the card into the card reader, then attach the card reader to the computer through a USB port. The card is visible as another drive on the computer, with the Lowrance files on it. For users of the Fugawi Moving Map Software, the most recent upgrade includes a utility which allows Fugawi to read the Lowrance files directly, and import and use them as any other waypoint and track data. This is a simple and handy way of moving spatial data into Fugawi.	The 76C has two interface ports available, one USB and one serial. The serial port functions the same as on other Garmin receivers (including the eTrex), and requires an optional cable, which costs about $30. The serial interface cable for the 76C is the same as for the III+ and V. The 76C comes with a USB cable and USB device drivers, together with "Trip and Waypoint Manager" software which allows a certain minimum of data exchange. As with the iFinder, the most recent upgrade for Fugawi Moving Map Software now includes "Garmin USB" as a Model selection in GPS Settings. With that selected, downloads and uploads of waypoint, route, and track data proceed through the USB connection the same as they do through a serial connection, except much faster.

Battery Life: Tested with 2300 mAh nickel metal hydride rechargeable batteries. Unit takes 2 AA-size batteries. Manufacturer's Specification - up to 12 hours (alkaline batteries) with no power-saving features turned on. Actual tested life - 12 hours with WAAS enabled (by default) and no use of backlighting. Actual tested life with Titan III external antenna connected: 8 hours	Tested with 2300 mAh nickel metal hydride rechargeable batteries. Unit takes 2 AA-size batteries. Manufacturer's Specification - up to 30 hours (alkaline batteries) with WAAS disabled and minimal use of backlighting. Actual tested life - 24 hours with WAAS disabled and no use of backlighting. Battery life was not shortened to any detectible degree in a separate test with WAAS enabled.

A Closer Look at Tracks and Trails . . .

For the natural resources management user, one of the most important uses of GPS technology is to traverse the perimeter of a topographic feature, overlay the traverse on a map to determine its location, and calculate the area included within the traverse. This is done with the track (trail in Lowrance) feature, by starting with an empty track log at the beginning of a traverse, adding points to the track log around the perimeter, and then saving the string of collected points to a discrete file (or by stopping the accretion of points to the current track). The track file thus created is downloaded to software that interprets the sequence of points, and connects the points from beginning to end (exactly like a gigantic dot-to-dot puzzle). The same software usually allows the track to be displayed against a background digital map, and calculates the area enclosed within the track.

As noted above, tracks can accumulate points until they reach some maximum number. The faster that points are added (called "the update rate") to the track, the sooner it will reach this maximum number, and the shorter will be the length of the perimeter that can be traversed. The update rate in both the iFinder and the 76C can be adjusted to either spread the points farther apart to conserve space and lengthen the perimeter, or to compress the points closer together to increase precision and shorten the perimeter. In both models the update rate can be set in terms of either time (seconds between points) or distance (in hundredths of a mile, 1/100 of a mile being about 53 feet).

The natural inclination is to set the update rate as close as possible, to increase the precision to the maximum. This, however, can become counterproductive because of the random Circular Error Probable (CEP) inherent in GPS position calculations, and cause points in the track to overlap, causing a condition known in GIS terminology as an "intersection". (See illustration below) Assuming a maximum CEP of 15 meters, the update rate should be set at 100 feet (.02 mile) or more to avoid these intersections. The question now arises, "How much does the .02 mile update rate limit the length of perimeter that can be traversed within one track?"

Referring again to the comparison of track capacity, we see that the 76C has the smaller capacity of the two, with Saved Tracks limited to 500 points. Coincidentally, the iFinder would also have just a little over 500 points in each trail, if its total track log capacity of 55,000 points were divided evenly among the 99 possible trails. With the update rate set at .02 mile, the total perimeter that can be traversed with 500 points is 52,800 feet, or 10 miles, which - if circular - calculates to 5,000 acres. For the vast majority of natural resources operations, this is a huge piece of real estate, and suggests that for nearly all natural resources work, 500 points in a track log is entirely adequate.

For those comparatively rare instances where the perimeter to be traversed exceeds the 500 point limit, there are adequate alternatives:

1. In the iFinder, increase the number of points in the trail to 9,999, or in the 76C, use and download the Active Track without saving it to a Saved Track. A track log of 10,000 points with an update rate of .02 mile will traverse up to 2 million acres.

2. In either model, collect a sequence of partial tracks, and use software - which can be as simple as NotePad - to connect the partial tracks.

3. Reduce the update rate to spread the available points over a longer perimeter. With large acreages the error introduced in this manner is trivial, amounting to only a fraction of a percent.

It appears, therefore, that either the Lowrance iFinder Pro or the Garmin GPSMAP 76C is entirely adequate for traversing and mapping natural resources projects, up to and including extremely large areas.

Illustration Showing an Intersection in a Track Caused by the Update Rate Set Too Close.

Graphic showing how GPS positions collected too close together can create intersections in the track.

Area Calculation Test

To determine the area enclosed within a given traverse is one of the more important uses of GPS technology in natural resources management. To test the inherent precision of the two receivers to collect accurate tracks and the ability of the software to calculate acreages from those tracks, two test areas were selected. The first was a small field of unknown acreage adjacent to NIFC, in Boise, Idaho. The second was a regular, rectangular one-half section of 320 acres, located east of Emmett, Idaho.

In the first test, the small field was traversed three times, once each with the Garmin 78C, the Lowrance iFinder, and the Garmin eTrex. In the eTrex the Active Track thus collected was saved to a Saved Track prior to downloading. To provide for a test standard, the background map DOQQ o43116e21 (Boise South NW) was displayed in Fugawi Moving Map Software, the small field carefully digitized on the background map, and its acreage calculated. Then the track(s) from each receiver were downloaded to the same software and the acreage calculated. Additionally, the 76C receiver has a utility onboard which will calculate acreage of a track, and that was tested, as well. The following table shows the results:

Source of the Track	Number of Points in Track	Calculated Acres	% Departure from Standard

Digitize from Software	25	5.5
eTrex Active Track	30	5.3	3.6
eTrex Saved Track	8	5.44	1
iFinder Pro	69	5.3	3.6
Garmin 76C Active Track	40	5.36	2.5
Garmin 76C Internal Solution	40	5.4	1.8

The widest variation here is only 0.2 acres, which is astoundingly constant, in view of the fact that the receiver calculation error alone can cause variations greater than 35% in small areas. Because of this it is usually best not to rely on a GPS traverse for acreage calculations of less than five acres, but in this case the variation is within acceptable limits.

The second test was conducted in similar fashion, using the DRG background map, o43116h4 Northeast Emmett. The one-half section traversed is bounded on all four sides with paved roads, and the traverses were by vehicle. In order that the traverse would include as much of the entire half-section as possible, the active (amplified) external antenna was mounted on the extreme left side of the car's roof, and the traverse was driven in a clockwise direction as close to the centerline as was safe. The eTrex - having no port for an external antenna - was positioned on the extreme left side of the car's dashboard. The test standard was digitized in the software by placing one traverse point at the center of each street intersection and calculating the acreage. The onboard acreage utility of the 76C was not tested.

Source of the Track	Number of Points in Track	Calculated Acres	% Departure from Standard

Digitize from Software	6	320.2
eTrex Active Track	35	319.1	0.34
eTrex Saved Track	8	317.4	0.87
iFinder Pro	361	321.4	0.37
Garmin 76C Active Track	201	319.3	0.28

A minor (and easily correctable) problem was encountered with the iFinder Pro, in which the update rate was set at 1 new point per second, rather than updating on the basis of distance. This created (GIS) intersections at the (street) intersections, where it was necessary to slow down or stop for the turns. (See again illustration above) It was necessary to delete some of the points at the corners before the software could calculate the acreage, but deleting these redundant points does not reduce the integrity of the track. This does, however, emphasize the importance of setting the update rate out beyond the CEP of the receiver.

All of the above results of both tests (including the eTrex!) are within the acceptable standard for natural resources traverses of 4% (the old compass-and-chain standard). As is expected, the percentage of error becomes smaller as the area traversed becomes larger, even when the "larger" area is not especially large. A half-section is not especially large as natural resources operations go, but even at that size the acreage calculation errors are less than 1%.

Even though two tests do not represent exhaustive testing, the consistent results suggest that uncorrected data from inexpensive GPS receivers is satisfactory for natural resources purposes. More to the point of this review, either the Garmin GPSMAP 76C or the Lowrance iFinder Pro will collect track data from which is is possible to calculate an accurate acreage on sites of greater than five acres. In general, the 76C enjoys a slight advantage in ease of use - especially for occasional users - and the Lowrance has a substantial advantage in memory and storage of data, and they may both be regarded as satisfactory for natural resources purposes.

**In the Spring of 2005, Lowrance has brought out two additional models of the iFinder, the iFinder H2O and the iFinder Hunt, both of which are water resistant. Comparison of the specifications shows that they both have comparable features to the iFinder Pro, which is not water resistant and comes with an awkward little plastic bag for using in wet weather. The iFinder Hunt has a built-in electronic compass and barometric altimeter, at an additional cost of about $70. Best price on the Web for the "Plus" package of the H2O, as of April 14, 2005, is $269, the same as the current best Web price for the Pro. For the natural resources professional, the water-resistant feature of the H2O/Hunt makes either of them a better choice than the Pro.