Adjusting RTK base station coordinates with the JAVAD TRIUMPH-LS

November 23, 2015 - By GPS World Staff

By Matt Johnson

When a GNSS RTK base station is started by assuming an autonomous position, it is necessary and good practice to later adjust and correct the coordinates with a solution referenced from known coordinates. JAVAD’s field software for the TRIUMPH-LS, J-Field, has the ability to adjust the RTK base station coordinates and RTK points surveyed using corrections from that base station.

Three methods can be used to accomplish this.

Manually Entering New Base Station Coordinates

Base station coordinates can be updated manually by entering new coordinates for the base station. These new coordinates can obtained through post-processing the base station data with OPUS or JAVAD’s DPOS web interface. Follow these steps to apply the corrected coordinate to the base station and adjust all the points from this base station through J-Field:

Select an RTK or base station point in the Points screen.
Tap on the blue screen displayed on the right side of this screen to view the Base Rover Statistics screen.
Tap the Base button and you will be prompted to enter the corrected coordinates for the base station.
Enter the new coordinates and tap OK.

J-Field will then search for all the points contained in the current project with the same original matching base station coordinates and apply offsets to adjust all these coordinates into the known coordinate system. The adjusted coordinates along with the original base station and surveyed origin coordinates will still remain stored in the database for documentation purposes and so that adjustments can be undone or modified if necessary.

Base Rover Statistics screen.

DPOS

When a Javad base station is started with J-Field using Base/Rover Setup, the raw GNSS data is automatically saved in the base station receiver. When the base station is then stopped with Base/Rover Setup, the data is downloaded into J-Field so that it will be available for post processing DPOS. To post-process the data, open the DPOS tool found in the CoGo menu and select the base file you wish to process. With the TRIUMPH-LS connected to the Internet, tap the DPOS button to upload the file to DPOS. This automated process will then update the base station and RTK surveyed points using the same algorithm described above.

Shift Mode

The newest feature of J-Field, Shift Mode, allows real-time corrections to be applied to receive base station corrections. A base station can be started with an autonomous position and then corrected by surveying a point with known coordinates. The known point could be a point previously surveyed with a base station setup in a different location. This feature is useful for several scenarios:

You need to move or “leapfrog” your base station to extend the radio range into a new area.
Your original base station point has been lost.
You wish to save time by starting the base station with it mounted to the top of your vehicle. Setting the base station and radio up on the top of vehicle by mounting it a roof rack or using a magnet mount saves time by eliminating the need to set up tripods and can help protect the base station from disturbances or theft in undesirable locations. For the best performance, the base station should be mounted in a level position so that phase center variations and antenna offsets are correctly applied. If you are parked on a sloped surface, it may be necessary to use a tribrach to level the receiver on the top of your car.

The Real-time Position Shift function can be accessed from the Setup menu under Advanced. In this screen, select a point you have collected RTK coordinates from with an autonomous base station, and then the known coordinates of this point. Check the Apply Shift and the shift will be applied to all the RTK surveyed points found in the current project collected from this base station. This shift will continue to be applied to all the points surveyed from this base station.

Position Shift screen.

Real-time Position Shift can also be accessed from the Collect Action screen by clicking the button below the Start button and changing the collection mode to Shift. In this mode, select the Known Point and then press Start from the action screen so that the offset can be calculated. After it has been calculated, you can apply the shift.