Utilising a standard G-858 MagMapper System the DGPS option can be added without any requirements for retrofitting of existing equipment.

Components to the G-858 Real-Time DGPS System :- There are two parts to the system.

• 1) A specially modified Trimble AG-132 DGPS Receiver, which has been through extensive demagnetisation re-design, and
• 2) an optional Parallel Swathing (Cross-Track Error Light-bar indicator) which is used to navigate the user down the line and to the start of the adjacent lines.

• 1) Locating the survey area :- With the survey area coordinates known from pre-survey planning, the user needs to locate the survey origin. This can be achieved either by following the current position shown on the AG-132 Receiver LCD (2 line x 16 character panel) when enroute to the site, which in addition to showing current real-time DGPS position also displays speed over ground, and course over ground, or by using an alternative surveying technique (eg. a separate hand-held DGPS, or conventional surveying.) The Trimble AG-132 was not intended to provide full featured, real-time navigation to the survey area, and there are no provisions for entering waypoint information.
• 2) G-858 MagMapper Setup :- After locating the survey area it can be useful, but not essential, to visually mark the survey origin, and endpoint of the first line (ie. Y=min, Y=max). Following this, setup the G-858 as normal, connecting the Trimble AG-132 to the G-858 console, and the Trimble Parallel Swathing Light-bar to the AG-132. Setup the parameters for survey grid for Mapped Survey Mode in the G-858. You are now ready to survey with real-time DGPS navigation!
• 3) GParallel Swathing (Cross-Track Navigation) OPTIONAL :- Move to the start of the first line. Press Button A on the AG-132. Start recording data as normal in the G-858 and move down the first line. At some point down the first line (or at the end of the first line) press Button B on the AG-132 keypad panel. This will immediately activate the parallel swathing guidance system, and create an imaginary infinite extension to the line. This is for steering purposes only and will provide cross-track error at 10Hz. At this point the entire line is held in memory and used as a base-line for all subsequent parallel lines. Now at the end of line, you can turn left or right, once you have pressed increment line. When you get to within 50% of the distance to the next line, the Parallel Swathing Option will ‘snap’ over to the next infinite line, and steer you to its respective start-of-line point. At the end of the second line there is no need to press any buttons, but rather you simply choose to go left or right and head that way until the guidance system signals a turn back towards the start of the next line.
• 4) Operating without the Parallel Swathing Option :- If only the AG-132 is used the operator will still enjoy the benefits of differentially corrected real-time information recorded with the standard magnetic data, however there will be no facility for online cross-track navigation and steering to adjacent lines. The main point though is that all location information would still have been derived via real-time sub-metre DGPS data from the Fugro Omnistar™ Service