RTK (Real Time Kinematics), VRS (Virtual Reference Station), PPP (Precise Point Positioning), and SSR (State Space Representation) are different methods used in Global Navigation Satellite Systems (GNSS) to achieve high-accuracy positioning.
RTK traditionally uses the nearest base station to provide correction data. A single receiver uses the nearest single base station.
VRS relies on a network of reference stations to simulate a virtual base station at the user’s location, offering RTK (Real-Time Kinematic) accuracy.
PPP uses precise satellite orbit and clock information to achieve accuracy, but it typically has a longer convergence time.
SSR, a newer technology, transmits corrections as discrete components for an entire region, allowing for efficient data delivery and potentially combining the strengths of both RTK and PPP.
VRS (Virtual Reference Station):
How it works:
A network of GNSS reference stations is used to calculate corrections for the user’s location. These corrections are then transmitted to the user’s receiver, creating a “virtual” reference station at their position.
Key features:
– Achieves RTK-level accuracy (centimeter-level).
– Requires a bidirectional communication link between the user and the service provider, as the user’s approximate location is needed to generate the virtual base station.
– Generally limited to the coverage area of the reference station network.
– VRS is typically used for applications requiring high accuracy like surveying and construction.
PPP (Precise Point Positioning):
How it works:
PPP relies on precise satellite orbit and clock data, along with models for atmospheric delays, to calculate corrections. These corrections are then applied to the user’s GNSS receiver’s data.
Key features:
– Can achieve high accuracy (centimeter-level) but typically requires a longer convergence time (several minutes to tens of minutes) compared to RTK.
– Does not require a nearby reference station, offering global coverage.
– Generally a simplex data connection (one-way from the service provider to the user) is sufficient.
PPP is well-suited for applications where high accuracy is needed, but a fast convergence time is not critical.
SSR (State Space Representation):
How it works:
SSR corrections are broadcast as separate components for a larger area, allowing receivers to combine them based on their specific location.
Key features:
– Enables efficient data delivery and can potentially combine the benefits of RTK and PPP.
– SSR corrections are typically valid for an entire service area, requiring no user input of location for corrections.
SSR can be used in conjunction with other techniques like PPP to achieve higher accuracy.
– SSR can be a good option for applications requiring both accuracy and efficient data transmission.
Summarizing:
VRS offers the highest accuracy (RTK level) but requires a nearby reference station and bidirectional communication.
PPP offers global coverage and high accuracy, but with longer convergence times.
SSR aims to combine the best of both worlds, offering efficient data delivery and potentially high accuracy for large areas.
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