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More expensive mapping grade systems can produce sub-meter level horizontal accuracies, with generally variable and unreliable vertical (elevation or altitude) acccuracies. The user must occupy each point for a brief time to collect data before a location is obtained. These systems are suitable for mapping natural resources such as timber, farmland, wetlands/marsh and are less affected by "canopy" than survey grade technologies. Decimeter level horizontal accuracies can be obtained with "post processing". Some expertise and training are required.
Survey grade systems come in 2 basic types: single frequency and dual frequency. With single frequency systems, data collection is slow and data collected must be "post processed" before the location information is obtained. Occupation times are long-generally 45 minutes to several hours. These systems are useful only for establishing control.
This type of surveying with a single frequency system is called "static" mode GPS surveying. Some single frequency systems can collect data in static or Post- Processed Kinematic (PPK) mode, but the rate of data collection cannot compare to that produced by dual frequency systems. Also, if the single-frequency unit loses its signal when operating in PPK mode, it takes some time to re-initialize before survey work can begin again.
Dual frequency systems only require post-processing when operating in static or "fast static". . In Real Time Kinematic (RTK) GPS, the positional data are displayed and recorded immediately. Subcentimeter to millimeter level accuracies (both horizontal and vertical) are obtainable with both single and dual frequency technologies. To obtain true latitude, longitude, and elevation for new points, both systems need to occupy existing established control monmentation. Considerable skill, training, and expertise are required to operate either type of system effectively.
SECI’s System:
SECI currently uses the state-of-the-art Trimble 4800/4700 series RTK GPS system. In our hands, the accuracy, speed, and productivity of this system is unparalleled for survey grade work. Our system can function in either static or RTK mode. In RTK mode, SECI personnel can collect survey grade data rapidly. For engineering design quality topographic mapping, our ATV mounted system can collect up to a few thousands points per day over open ground.
Our Trimble data collection system is fully integrated with our conventional total stations. Our data collector can be "unplugged" from the GPS receiver and "plugged" into the total station and plugged back into the GPS receiver, allowing us to use the same survey software and the same file to compile "infill" in areas where satellites observations are obstructed by trees, tall buildings and the like. The completed data file is then downloaded to our field laptop or office computer either for plan preparation or to be e-mailed directly to our client.
Advantages of SECI’s RTK GPS Systems
GPS APPLICATIONS
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