Reviews > Navigation and Map Gear > GPS > Delorme Earthmate GPS LT-20 > Brian Tannehill > Field Report

Backpacking Background:

I am fairly new to backpacking, but I have hunted/fished/camped all my life in East Texas, Colorado, and California. My young kids (4, 10, 12) limit me to weekend overnight camping trips, or day hikes Geocaching. I am also an avid mountain biker. For now I live in the Central Coast area of California (Lompoc, Santa Maria area), and am surrounded by many different areas from beaches to mountain regions ranging up to 5,000 feet (1,500 m), with the temperatures averaging about 60 F (16 C) degrees year round.

Product Information:

Manufacturer: Delorme
Year of Manufacture: 2005
URL: http://www.delorme.com
Software: Delorme Street Atlas USA 2005
MSRP: $99.00 US
Weight: 2 5/8 oz (76 g)
Length of Cable: 5 feet (1.5 m)
Size of Unit: 2 5/8 in (6.6 cm) long x 1 7/8 in (4.8 cm) wide x 9/16 in (1.5 cm) thick

Minimum System Requirements:

The system requirements for the Earthmate GPS is a USB port on my laptop.
The system requirements for Street Atlas 2005 are:
Microsoft® Windows® 2000 (Service Pack 3 and higher): 64 MB RAM (256 MB recommended)
Microsoft Windows XP: 128 MB RAM (256 MB recommended)
Intel® Pentium 300 MHz or higher processor (600 MHZ recommended)
700 MB of available hard-disk space
Microsoft Internet Explorer 5.01 or later
32x CD Drive
Microsoft Windows 98/ME is not supported with this release

My System:

I am using a Dell Inspiron Model 5100 laptop with a Pentium 4, 2.4 GHz, and 256MB of RAM running Windows XP Home.

Field Locations:

The locations of my tests will range from the Los Padres National Forest just east of here ranging up to 5000 feet (1500 m) in elevation to the locally famous Pismo Beach. Other areas I will be driving include Santa Maria, Lompoc and monthly trips down to Agoura Hills just north of Los Angeles. Basically anywhere I drive on the central coast of California.

Field Report:

After two months of use, I still really like this program. Read my Initial Report for the initial questions I had on the software.

I'll try to explain the GPS stuff here. On the main GPS screen there is a Sat info button. This shows the Dilution of Precision, Satellite listing, and the Almanac.

© 2004 DeLorme (www.delorme.com) Street Atlas 2005®

DOP
From the glossary in Street Atlas, it defines Dilution of Precision (DOP) as the total effect of all error sources in locating a position.

This program uses three types of DOP's, Horizontal (HDOP), Vertical (VDOP), and Position (PDOP). Definitions form the glossary:

HDOP
The measure of how much the geometry of the satellites affects the horizontal position estimate.

PDOP
The measure of how much the error in the position estimate produced from satellite range measurements is amplified by a poor arrangement of satellites (with respect to the receiver antenna).

VDOP
The measure of how much the geometry of the satellites affects the vertical position estimate.

Basically for GPS to work, I need three satellites for position, and a fourth for altitude. Think of a map when trying to triangulate a position. I want to get reference points that are 90 degrees from each other instead of three areas within a small angle. The same thing goes for GPS. I want 4 satellites that are 90 degrees of each other with one being directly overhead. This is what Dilution of Precision is, the measure of the angular separation.

Here is a table that shows which values are acceptable for DOP. The higher the value, the less accurate the GPS.

Quality	DOP
Very Good	1-3
Good	4-5
Fair	6
Suspect	>6

Satellite Listing
The next tab is the satellite listing. This shows the satellite number in view, the azimuth (az) 0-360 degrees like the face of a compass, elevation (elv) how high above the horizon, and signal strength measured in decibels (db).

Almanac
The satellite almanac tells the receiver basic orbital information. An example would be az and elv of the sat. Normally a new almanac would also take 12 minutes to download so if your GPS has been turned off for a while it could take a few minutes to download the new almanac.

More Field Usage

Route function
This has been one of the biggest problems with mapping software, keeping roads up to date. There is one road outside my house that has been closed now for over 6 years. However this is not reflected in the software. The good news is I can go in and manually edit that road as closed and then save it. Now when I route from my house it avoids that road.

Another cool function of the GPS is it will automatically re-route me back on track when I get off course. I can set the program to wait and recalculate my route after I am so far off course or I can leave it at the default setting which is 300 feet (90 m). With the back on track feature set to 300 feet (90 M), I find that making quick turns inside the city gets the software behind. So to fix this I set the back on track feature to 100 feet (30 M). The problem with this are the roads in the digital map does not always correspond with the location as reported by the GPS. While driving south on Hwy 101, the road and the GPS track constantly venture from each other, sometimes in excess of 200+ feet (60 m). So I keep the setting at 300 feet (90 M). If need be I can quickly go in and update the value to 100 feet (30 m).

Turn by Turn
Another cool feature of the software is the voice commands for each turn. The 2006 Street Atlas version also has a feature that lets me select how far out it will tell me of the upcoming turn. I leave this at 30 seconds. I also believe that the software does not use the actually speed of the GPS for time calculations. It uses the actual hard coded road speeds under the route function. I have changed the speeds while in route and it has reflected the update time. I would like it better if it used the GPS speed, that way if I hit traffic or slow down it will update and correct.

I have used this software over much of central California. I drove to Bakersfield with it and was disappointed with its Point of Interest (POI) database. You see Bakersfield has the closest Sonic Restaurant and that is about 2.5 hours away. So I plotted our course and away we went. It guided me flawlessly right into a residential neighborhood with no Sonic in site. So we backtracked a few miles to another location hoping that it was right, which it was. The neighborhood looked like it had been there for a while, not one of those popcorn neighborhoods.

Other than that one mistake, I've used the software for numerous Geocaching hunts, and it takes me right to the trailhead or as close as I can get to it. I've also used it traveling down to Agoura Hills (about 2.5 hours) to go shopping at some local stores. I just input the address and it took us right to it. On the way back, I used the POI feature to find an Outback restaurant (the closest one of those is also 2 hours away) using the GPS radar function. It found one less than 10 minutes away from our position on Hwy 101, gave us the phone number, and we called and made reservations.

I really like the GPS radar function. It sweeps the area ahead of me at a distance I set. It will also repeat its search every few minutes as I travel down the road. I can choose whatever I want it to look for, like a restaurant, gas station, etc.

There are a few quick tabs across the top of the screen for things like creating a route, starting the GPS, and some options. I like it, but since I'm not used to them being up there, I don't use them. Its almost like everything is focused at the bottom of the screen so I do not pay attention to the top.

Some of my questions and concerns:

I still have not figured out "how much power" is used by the GPS, but I do notice my battery runs out quicker while using it. Maybe something I will look for in the long term report.

There is a lot of information to digest/use for this software, and I find myself having trouble remembering where exactly I found that cool feature. There should always be a second person to either drive or work the software, I would not want to do this by myself. Not really a question but just a concern at this point.

I find myself putting the laptop down after I get on a long stretch of road. I find it most useful in city traffic or if I am actively looking for something.

Test Plan:

I will continue to use this software where ever I go in Central California. It is performing as expected so far, and I really like it. Brian

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Reviews > Navigation and Map Gear > GPS > Delorme Earthmate GPS LT-20 > Brian Tannehill > Field Report