# GNSS Master

GNSS Master is a free Android app developed by ArduSimple that acts as a universal bridge between an external GNSS receiver and any Android application. It connects to receivers via USB OTG, Bluetooth, BLE, or Wi-Fi/TCP, streams RTK corrections from an NTRIP caster like RTKdata.com, and provides the corrected position to other apps through Android mock locations. This makes it one of the most versatile NTRIP relay apps available — any Android app that uses location (Google Maps, ArcGIS Field Maps, DroneDeploy, etc.) can benefit from centimeter-level accuracy without needing its own NTRIP support.

**Download:** [Google Play Store](https://play.google.com/store/apps/details?id=com.gnssmaster) (free)

## Key capabilities

| Feature                    | Details                                                                               |
| -------------------------- | ------------------------------------------------------------------------------------- |
| **Platform**               | Android (phone or tablet)                                                             |
| **Cost**                   | Free (PointPerfect corrections require a separate subscription from ArduSimple)       |
| **Receiver connection**    | USB Serial (OTG), Bluetooth Classic, Bluetooth LE, Wi-Fi / TCP                        |
| **NTRIP support**          | Built-in NTRIP Client (V1 and V2)                                                     |
| **Mock location relay**    | Yes — broadcasts corrected position to all other Android apps                         |
| **NTRIP Server mode**      | Yes — can also function as an NTRIP server for base station setups                    |
| **Receiver configuration** | Can change u-blox and Septentrio receiver settings (Rover, Base, custom config files) |

## Requirements

* Android phone or tablet with USB OTG or Bluetooth
* External GNSS receiver (ArduSimple simpleRTK2B, SparkFun RTK Facet, any u-blox F9P board, Septentrio, etc.)
* Internet connection (cellular data or Wi-Fi)
* Active RTKdata.com account with RTK credentials

{% hint style="info" %}
Don't have an RTKdata.com account yet? [Start 30-day Free Trial](https://rtkdata.com/try-rtk-corrections-free-for-30-days/) or [View Pricing](https://rtkdata.com/pricing/)
{% endhint %}

## Step-by-step setup

{% stepper %}
{% step %}

#### Connect your GNSS receiver

1. Connect your GNSS receiver to your Android device:
   * **USB OTG:** Plug the receiver into your phone/tablet using a USB OTG cable. Grant USB permission when prompted.
   * **Bluetooth:** Pair the receiver in Android Bluetooth settings first, then select it in the app.
   * **Wi-Fi/TCP:** Ensure both devices are on the same network.
2. Open **GNSS Master**. Access the navigation drawer by swiping from the left edge or tapping the GNSS Master icon in the top menu bar.
3. Go to the **Receiver** page and tap the **gear icon** next to **GNSS Receiver Connection**.
4. Select your connection type (USB Serial, Bluetooth, BLE, or TCP) and choose your device from the list.
5. Tap **Connect**. The status should change to **Connected** with data flowing.

{% hint style="warning" %}
For USB OTG connections, your Android device must support USB Host mode. Most modern Android phones and tablets do. If the receiver is not detected, try a different USB OTG cable — some charge-only cables do not support data.
{% endhint %}
{% endstep %}

{% step %}

#### Enable mock location output

To relay the corrected position to other Android apps:

1. On your Android device, go to **Settings > About Phone** and tap **Build Number** 7 times to enable Developer Options.
2. Go to **Settings > Developer Options > Select mock location app** and choose **GNSS Master**.
3. In GNSS Master, check the **Mock Location** checkbox on the main screen.
4. Optionally, also check **Output to SW Maps** if you use SW Maps for data collection.

{% hint style="info" %}
With mock location enabled, every Android app on your device will use the RTK-corrected position from your external receiver instead of the phone's internal GPS. This includes Google Maps, any GIS app, and field data collection tools.
{% endhint %}
{% endstep %}

{% step %}

#### Configure the NTRIP correction source

1. Open the **Corrections** page by tapping **Correction Input** or navigating via the drawer.
2. In the **Mode** dropdown, select **NTRIP Client**.
3. Tap the **+** button next to **NTRIP Connections** to add a new profile.
4. In the NTRIP Client dialog, enter the following:

{% tabs %}
{% tab title="North America" %}

* **NTRIP Address (Host):** `rtk.rtkdata.com`
* **IP Fallback:** `13.56.117.10`
* **Port:** `2101`
* **Username / Password:** From *RTK Credentials* in the internal dashboard (not website login)
* **Mountpoint (ALL CAPS):** `AUTO` (recommended) — or `AUTO_WGS84`, `AUTO_ITRF2020`, `AUTO_ITRF2014`
  {% endtab %}

{% tab title="Europe" %}

* **NTRIP Address (Host):** `eu.rtkdata.com`
* **IP Fallback:** `3.73.41.96`
* **Port:** `2101`
* **Username / Password:** From *RTK Credentials* in the internal dashboard (not website login)
* **Mountpoint (ALL CAPS):** `AUTO` (recommended) — or `AUTO_WGS84`, `AUTO_ITRF2020`, `AUTO_ITRF2014`
  {% endtab %}

{% tab title="Australia" %}

* **NTRIP Address (Host):** `aus.rtkdata.com`
* **IP Fallback:** `54.206.56.130`
* **Port:** `2101`
* **Username / Password:** From *RTK Credentials* in the internal dashboard (not website login)
* **Mountpoint (ALL CAPS):** `AUTO` (recommended) — or `AUTO_WGS84`, `AUTO_ITRF2020`, `AUTO_ITRF2014`
  {% endtab %}
  {% endtabs %}

5. Check **Send NMEA GGA to Base Station**. This is required for RTKdata.com's VRS corrections.
6. Tap **Save**.

{% hint style="danger" %}
**"Send NMEA GGA to Base Station" must be checked.** Without GGA, RTKdata.com cannot determine your position and cannot generate Virtual Reference Station corrections. You will stay on FLOAT indefinitely.
{% endhint %}
{% endstep %}

{% step %}

#### Connect and verify RTK Fix

1. Select your saved NTRIP profile and tap **Connect**.
2. In the **Status** page, verify that both **GNSS Receiver Connection** and **Correction Input** show **Connected** with data flowing.
3. Monitor the solution status as it progresses: **Autonomous > Float > Fix**.
4. Once you see **RTK Fix**, the corrected position is being relayed to all apps via mock location.

{% hint style="info" %}
Convergence to Fix typically takes 15–60 seconds under clear sky. The NTRIP client stays connected even when the receiver temporarily disconnects, so corrections resume automatically when the receiver reconnects.
{% endhint %}
{% endstep %}
{% endstepper %}

## Vertical reference (heights)

{% hint style="info" %}
Heights from RTKdata.com are **ellipsoidal**, not orthometric (mean sea level). If your workflow requires orthometric heights, apply a geoid model in your GIS or surveying software.
{% endhint %}

## Troubleshooting

| Problem                                 | Cause                                | Fix                                                                                      |
| --------------------------------------- | ------------------------------------ | ---------------------------------------------------------------------------------------- |
| USB receiver not detected               | USB OTG not supported or bad cable   | Use a data-capable USB OTG cable. Check that your Android device supports USB Host mode. |
| Bluetooth pairs but no data             | Wrong receiver protocol or baud rate | Ensure the receiver outputs NMEA over Bluetooth. Check baud rate settings.               |
| NTRIP connects but stays on Float       | GGA not sent to caster               | Check **Send NMEA GGA to Base Station** in the NTRIP profile settings.                   |
| Mountpoint error                        | Wrong capitalization                 | Type `AUTO` in ALL CAPS. Do not use `auto` or `Auto`.                                    |
| Mock location not working in other apps | Developer Options not configured     | Verify GNSS Master is selected as the mock location provider in Developer Options.       |
| Corrections drop when screen turns off  | Android battery optimization         | Disable battery optimization for GNSS Master in Android settings.                        |

## Tips for best results

* **GNSS Master is the best option for relaying RTK to any Android app.** If your field app does not have a built-in NTRIP client, use GNSS Master as the relay layer.
* **You can browse the mountpoint source table** by tapping the button next to the mountpoint field. However, for RTKdata.com, simply type `AUTO` in ALL CAPS.
* **Receiver configuration built in.** You can switch your u-blox F9P between Rover and Base mode directly from the app — no need for u-center on a desktop.
* **Works alongside SW Maps.** Enable both Mock Location and "Output to SW Maps" for the best combination of NTRIP relay and GIS data collection.
* **NTRIP V2 is supported** if your caster requires it. Select the version in the NTRIP connection dialog. RTKdata.com works with both V1 and V2.