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A Little GPS that could...

One of the common options of modern GPS receivers is a plotter screen.Waypoints, Icons and tracks can be displayed on that screen, so the user can see a graphical representation of his position in reference to various locations. Some of the more expensive, modern receivers can display factory or user-loaded maps that are fairly detailed. Less expensive receivers donít have that option, but as long as your receiver has a plotter screen and you are willing to invest a little time, you CAN display a map on the screen.Lets face it, the map is not going to be the prettiest one, but itís going to be usable for quick reference.

Some receivers will allow you to display icons as well as waypoint names/numbers to display a position on the plotter screen. Some allow you to display segments of plot trails as isolated sections, while some don't. The system described below is the one I use with an Eagle Expedition II. In fact, the large memory of the EEx2, which allows you to use the described technique, was one of the deciding factors in my receiver selection. Note that the EEx2 is no longer manufactured, but its Lowrance sibling, the GlobalNav 212 has even more memory. In any case, the method I use can be easily  adapted to just about any make and receiver model.

Besides the receiver, it's necessary to use some software which allows you to display maps, create plots, waypoints and icons and then transfer them to the receiver. I use OziExplorer which can work with DRG, BSB, or scanned maps.

The most natural way of displaying a map would be by displaying plot trails; after all they show on the screen as lines. However, there are a couple of problems associated with this.

If your receiver is capable of using only one plot trail and you want to use it for a map display, then you will have to turn off the logging. Otherwise the drawn map would be progressively replaced with the updated plot of your current trip. If you use a receiver like an EEx2, GN212 or GIII, you can use the savable plot trails for map display.

The second problem with using plots for a map display lies in the way some receivers display the plots. For example Garmin units are capable of displaying a plot where a line between unrelated sections is not visible. Lowrance receivers display all the plot segments. Thus, a figure "H" traced in OziExplorer and uploaded to a Lowrance / Eagle receiver, would normally show in the following fashion:

Sure it looks like a double letter N figure. If a road from Pt# 2 to Pt# 3 doesn't exist, the display like the one above would not be very helpful. The workaround is very simple. The plot can be created as:

OziExplorer is almost indispensable for creating plots as such. During the creation of the plot, it allows the user to "snap to" existing plot points, so there is no risk of showing double lines.

The next important feature that can be utilized in drawing maps is an Icon. One of the Icons used by LEI receivers is a small cross. It's so small that it almost looks like a dot on the display. A number of them placed on the map feature border can easily represent it on the GPSR screen.

Let's look again at the map of Andrealand.

 

Red crosses are the Icons. The red line at the bottom of the map is a plot trail. Since the trail has a number of legs, the same technique as for drawing the "H" figure was used.

Without the topo map background, the same screen looks like this:

The separation of 150 - 200 meters between the individual icons was dictated by the screen resolution of the EEx2. It is optimized for a zoom level of 2 - 3 kilometers. Placing the Icons at smaller intervals would create too much clutter. You might find that different spacing is more suited to your needs and your receiver. Just do a little experimenting before creating maps with many details.

The above creation results in the GPS receiver displaying a map that in my opinion is suitable for quick visual reference.

  

So far the only other option to display your own maps on the GPS receiver screen is to spend  more money and get a GlobalMap 100 receiver and OziMC, but that's a story for a different article. If you want to catch a glimpse of some GM100 screens displaying OziMC-created maps, you can see some samples and links to more in the G3+ vs GM100 article.

 

Andrew Kalinowski

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