# CORs/VRS vs Base Stations

## Reference Stations

CORs (Continuously Operating Reference Stations) and VRS (Virtual Reference Stations) are sources of GNSS corrections. These can be reached in real time for use as RTK corrections. Data from CORs/VRS are posted online, and available to download for use in PPK corrections after your drone flight.

* Delivers GNSS corrections via internet from a network of reference stations.
* Ideal for urban or connected environments with reliable cellular or Wi-Fi.
* Simplifies setup, no need to carry extra hardware.
* Requires a subscription in many cases; accuracy depends on baseline distance to nearest station.
* Best suited for RTK workflows, but can support PPK if raw data is logged. 

***

## Local Base Station

A local base station is a physical GNSS receiver that will be set up at each survey site. Base Stations can be used in both RTK and PPK workflows. For RTK workflows, base stations use a ground radio or other such connection to deliver real time corrections. For PPK workflows, base stations log rinex data to be used in post processing.

* A physical GNSS receiver placed at a known location near the survey site.
* Offers higher accuracy due to short baseline and full control over setup.
* Works well in remote areas without internet access.
* Requires additional equipment and setup time.
* Supports both RTK (real-time corrections) and PPK (post-flight processing). 

***

## Comparison

| Feature             | Reference Stations         | Local Base Station            |
| ------------------- | -------------------------- | ----------------------------- |
| Connectivity Needed | Internet (cellular/Wi-Fi)  | None (radio or direct link)   |
| Setup Complexity    | Minimal                    | Moderate to High              |
| Accuracy            | Good (depends on baseline) | Good (depends on setup)       |
| Cost                | Subscription based         | One-time equipment investment |
| Best Use Case       | Urban, connected sites     | Remote, unconnected sites     |


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