# Coordinate Systems & Datums

RTKdata corrections are available in multiple geodetic reference frames. The mountpoint you choose determines the coordinate system of the corrections streamed to your device.

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## Mountpoints

RTKdata provides four mountpoints. Names are **case-sensitive** and must be entered in **ALL CAPS**.

| # | Mountpoint          | Details                                                                                                                                           |
| - | ------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------- |
| 1 | **`AUTO`**          | Regional Geodetic Coordinate System (RGCS) — automatically delivers corrections in your region's local datum. **Recommended for most workflows.** |
| 2 | **`AUTO_ITRF2020`** | ITRF2020 Geodetic Coordinate System at epoch 2015.0                                                                                               |
| 3 | **`AUTO_ITRF2014`** | ITRF2014 Geodetic Coordinate System with current epoch                                                                                            |
| 4 | **`AUTO_WGS84`**    | WGS84(G2139) in the middle of the current year (e.g., 2025.5 for year 2025, 2024.5 for year 2024)                                                 |

> **Recommendation:** Use `AUTO` unless your project specifically requires a global reference frame. AUTO eliminates the most common source of coordinate shifts by delivering corrections in your regional datum.

***

## Regional Geodetic Coordinate System (RGCS)

When you connect with the `AUTO` mountpoint, RTKdata automatically selects the correct regional geodetic coordinate system based on your location. The table below shows exactly which datum and epoch is delivered per region.

| #  | Geodetic Coordinate System Name            | Epoch #       | Effective Regions    |
| -- | ------------------------------------------ | ------------- | -------------------- |
| 1  | **NAD83(2011)**                            | 2010.0        | USA                  |
| 2  | **NAD83(PA11)**                            | 2010.0        | USA Hawaii           |
| 3  | **NAD83(MA11)**                            | 2010.0        | Guam                 |
| 4  | **NAD83(CSRS)v7**                          | 2010.0        | Canada               |
| 5  | **ETRS89(ETRF2010)(2010.0)**               | 2010.0        | Europe               |
| 6  | **GDA2020(2020.0)**                        | 2020.0        | Australia            |
| 7  | **NZGD2000(2000.0)**                       | 2000.0        | New Zealand          |
| 8  | **TUREF(2005.0)=ITRF96(2005.0)**           | 2005.0        | Turkey               |
| 9  | **ITRF2008(2005.0)=ITRF2008(2005.0)**      | 2005.0        | India                |
| 10 | **ITRF2008(2011.811)**                     | 2011.811      | Egypt                |
| 11 | **NGD2012(2012.0)=ITRF2008(2012.0)**       | 2012.0        | Nigeria              |
| 12 | **PGD2020=ITRF2014(2020.044)**             | 2020.044      | Philippines          |
| 13 | **ITRF2014(2010)**                         | 2010.0        | Mexico               |
| 14 | **ITRF2014**                               | current epoch | Kenya                |
| 15 | **CGCS2000(2000.0)=ITRF97(2000.0)2**       | 2000.0        | China                |
| 16 | **JGD2011(2011.3945)=ITRF2008(2011.3945)** | 2011.3945     | Japan                |
| 17 | **IGRS2013(2012.0)=ITRF2008(2012.0)**      | 2012.0        | Indonesia            |
| 18 | **ITRF1991(1994.0)**                       | 1994.0        | South Africa         |
| 19 | **WGS84(G730)(1994.0)**                    | 1994.0        | Sri Lanka            |
| 20 | **ITRF2020(2025.0)**                       | 2025.0        | Taiwan               |
| 21 | **ITRF2014(2010)**                         | 2010.0        | Thailand             |
| 22 | **KGD2002(2002.0)=ITRF2000(2002.0)**       | 2002.0        | South Korea          |
| 23 | **MGRF2020(2020.0)=ITRF2020(2020.0)**      | 2020.0        | Malaysia             |
| 24 | **MTRF2000(2004.0)=ITRF2000(2004.0)**      | 2004.0        | United Arab Emirates |
| 25 | **SIRGAS2000(2000.4)=ITRF2000(2000.4)**    | 2000.4        | South America        |
| 26 | **GGD=ITRF2008(2011.353)**                 | 2011.353      | Georgia              |
| 27 | **WGS84(G2139)(20xx.5)1**                  | 20xx.5        | Other regions        |

> **Note:** For regions not listed above, `AUTO` falls back to WGS84(G2139) at the mid-year epoch.

***

## Why Your Coordinates May Be Offset

If you see a consistent **50 cm – 1 m offset** compared to local survey control, this is almost certainly a **datum mismatch**, not an accuracy problem.

The earth's tectonic plates move. Global frames like ITRF2014 track current plate positions, while regional datums (NAD83, ETRS89, GDA2020) were fixed at a specific point in time. The difference grows every year.

**This is not a bug — it's physics.**

**The Fix:**

1. **Use `AUTO`** — it delivers corrections in your regional datum, eliminating the shift in most cases.
2. **Software transformation:** If you must use a global mountpoint (`AUTO_ITRF2020`, `AUTO_WGS84`), set your rover/drone software to transform from WGS84/ITRF to your local system.

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## Vertical Reference: Ellipsoidal vs. Orthometric Heights

RTKdata provides **ellipsoidal heights** (height above the WGS84 ellipsoid). These are NOT the same as:

* Mean Sea Level (MSL)
* Orthometric height
* Local vertical datum

To convert to orthometric heights, apply a **geoid model** in your software:

* **EGM96 / EGM2008** — global geoid models
* **OSGM15** — UK geoid model
* **GEOID18** — US geoid model
* **AUSGeoid2020** — Australian geoid model

Most surveying software and GIS applications can apply geoid corrections automatically when the correct vertical datum is selected.

See [Understanding Heights](https://docs.rtkdata.com/get-started/understanding-heights) for a detailed guide.

***

## US Survey Feet vs. International Feet

If you see a steady **\~4 ft / 1.2 m offset** in the United States, check your controller's unit settings. The difference between US Survey Feet and International Feet causes a noticeable shift at scale.

**Fix:** Set your controller/software project to use the correct foot definition for your state.