Using Reverse-Shift in J-Field

By Matt Sibole

One of the newest developments in J-Field, JAVAD GNSS’s onboard data collection software, is the Reverse-Shift. This feature will allow you to mount a base on a magnetic mount to the top of your vehicle, instead of putting your base on a tripod.

This is a good idea for several reasons. First, you won’t have to worry about your tripod sinking in hot asphalt. Second, you will not have to worry about your tripod fading on frozen ground that begins to thaw.

Figure 1. My TRIUMPH 2 base mounted above my driver-side door on the roof, with my 35-watt radio and antenna just to the left.

The way Reverse-Shift works is by starting your base on an autonomous position. Once your base has started transmitting, you can then go into your collect screen and change the point tab to shift. You then have the ability to select a known point (a previously surveyed or calculated point). After you have selected this known point, you can go and survey that known point.

Figure 2. The shift screen showing the known point (previously surveyed point).

When you hit OK as shown in Figure 2, this will take you back to the collect screen, and then it will allow you to survey that point. It will give you an warning screen that states, “You are in Base Shift Calculation Mode, Do you wish to continue?” You will then be able to collect a surveyed point on the previously surveyed or calculated point. It will then give you the position shift information.

Figure 3. The adjustment parameters for the base.

Hit Accept, and this will adjust your base position by the stated difference, allowing you to continue to work on the known coordinate system without setting your base on a known point.

Figure 4. Staking back out to the (known point) after the Reverse-Shift has been completed. Notice the DTT (Distance To Target) is 0.006. degrees.

At the end of the day, when you go back to your base, hit “Stop Base”. This will download the static data out of your base into your TRIUMPH-LS rover.

The next morning when the CORS data has been uploaded, you can then post-process your base data using DPOS (JAVAD’s Data Processing Online Service). With DPOS you can then adjust your base to the TRUE state plane coordinate of where your base was actually sitting. It will also adjust all surveyed points that were collected from that base position.

For more information on JAVAD’s J-Field software, the TRIUMPH-LS or other JAVAD GNSS solutions, please feel free to visit www.javad.com, email matt@surveyingky.com, or call 1-888-550-5301 or 1-408-770-1770.