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PCCC GIS I Exercise 2 (AV9.1) - Locate your car with GPS, map it with GIS v2, Apr 2007 - page 4 / 31





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While you're waiting for the receiver to locate itself, I recommend you spend a few moments with the small card in the case of each unit that summarizes the menu structure of the receiver. This will help you see how the unit is organized into 3 main parts: SYS to show satellite positions and their strength, DATA to collect vector data and NAV. I have not used the NAV aspects of GPS, but many fishermen, hikers, etc. probably find this aspect to be the most valuable aspect of GPS. Like the breadcrumbs of the Hansel and Gretel story, these features allow you to collect waypoints digitally, then use them to navigate your way back home.

  • Once the GPS unit has re-established connections with an adequate number of satellites (you will know this when the printout at the bottom of the screen starts showing a new lat- long position, rather than showing “Old Position”), navigate through SYS (you may need to press SYS several times to get to the right screen) Setup

Configuration Coordinates System to make sure you will be logging in lat-long coordinates.

  • Press Close to move back up toward the top of the menu structure at Setup.

Now you're prepared to start logging points. Go to the first vehicle.

  • Press the DATA button

Create new file appears in a box. The proposed file name appears on a line below the box. The convention will look something this example: R092922A. The letter R (or S) identifies the receiver being used. The first 2 numbers are month (September), then 2 numbers for date(the 29th), then 2 for time in hours based upon a 24-hour military system, relative to Greenwich Mean Time (GMT). For example, Eastern Daylight Time is 4 hours earlier than GMT; if it is 6 PM (1800 hours) in NYC, your GPS receiver will show 22 (for 2200 hours GMT). The last letter (A) is the unique identifier for this particular file; if another file were to be collected during this same hour (between 2200 and 2259

hours GMT)

  • With the

its file DATA

name would be R092922B.

  • >

    Create New File box highlighted,







appears, with options to make point, line or area features.

  • Select Point. You now have the choice of beginning log GPS locations NOW or LATER. For our exercise, select NOW and press ENTER. As soon as you do this, the GPS unit will start collecting points, (one per second) over your car.

Note - If satellite coverage falls below the minimum acceptable threshold (4 visible and strong), the unit will stop beeping and stop collecting points. This could happen if you're close to big trees or in the "shadow zone" of a large building. Press the SYS button to scroll to the sliding scale window that allows you to reduce the precision of the unit until it starts beeping and collecting points again. If this fails, you will have to move to an offset location, perhaps on the opposite side of the street or away from the wall of a building.

Once the unit starts collecting points, a screen labeled Point, with a line called Comment, appears with a pencil scrolling a line in the lower RH corner, giving you a running tally of the number of points being collected by the unit. Hold the unit steady for at least 100 seconds. The reason you want to collect this many points is because the more points the GPS unit collects, the better your calculated position will be after differential correction.

  • At the screen that says "Comment", press ENTER, and a screen with the alphabet appears. Use the scrolling keys and the ENTER key to type the name of the car owner. If you mis-type, highlight BKSP and backspace over your mistakes, then re-type correctly. Don’t panic if it takes you a long time…you can’t collect "too many" points. 4

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