PIX4Dcatch RTK device with own-hosted RTK base station - PIX4Dcatch RTK

PIX4Dcatch can be used with an RTK GNSS base stations to obtain RTK corrections. This is useful if there is no NTRIP coverage on the site, there is low-reliability 4G coverage or subscribing to an extra NTRIP service is not an option.

Important: Even when using a stand-alone RTK base station for NTRIP, Catch RTK still requires a 4G connection to do coordinate system transformations.


The base station is placed on a reference point with known coordinates. The corrections calculated by the base station are then transmitted to the RTK device with a real-time communication channel via the NTRIP protocol.

Note: Pix4D supported RTK devices does not support UHF or LORA radio-based communication

To set up an NTRIP service with an own-hosted base station, the following generic steps are needed.

  1. Select a reference point close to the site with known coordinates. The coordinates of the point can either be known a-priori or calculated by other methods, e.g. PPP, long observations, etc.
  2. Configure the base station to act as a base with the known reference in your preferred Coordinate Reference System.
  3. Configure the RTK base station to connect to the internet using 4G or WiFi. For 4G you will need to install a SIM card with an active data plan in your base station.
  4. Configure the NTRIP service to provide the corrections for PIX4Dcatch.

Configuring an Emlid base station

Emlid RS2, RS2+ and RS3 receivers are capable of acting directly as base stations and indirectly using the Emlid NTRIP caster service. Those devices support both 4G and WiFi-based communication, which enables them to act as an NTRIP provider for PIX4Dcatch. Below we describe a simplified procedure for setup. More details are available on the Emlid public online documentation

Configuring the Emlid NTRIP caster service

Emlid provides an NTRIP caster solution for free. This central service requires an internet connection is available for both the RTK base station and the RTK GNSS device. Setting up the caster is a one-time setting that can be re-used if needed.

Follow the following steps to set up the caster:

  1. Open a web browser and go to https://https://caster.emlid.com/app/mountpoints and sign in with the Emlid account.
  2. Manage mount points in the My mount points section. It is safe to use the default settings. Please save the name of the mountpoint and the corresponding password; these values have to be used to set up the base station.
  3. The My devices section shows the credentials that have to be used by the RTK devices. Please save these values.


Setting up the base station

To set up a supported (Reach RS2, RS2+ or RS3) Emlid RTK receiver as a base station, the Emlid Flow app can be used. Emlid Flow is freely available in the App Store and the Google Store. The setup procedure is the same for all devices and can be done on the field.

Initial configuration before first time using.

Tip: Download the app at the office with a stable internet connection.

Steps to do at each site.

    1. Connect the mobile phone to the RTK receiver via Bluetooth
    2. Start the Emlid Flow app and connect the base station
    3. Go to Base settings and define the base point coordinates and height offset. The following options are available. For more information please see the Emlid Rx documentation
      1. Manual entry - When you place the base over a known point
      2. Average SINGLE - position of the base is calculated from a SINGLE solution over a pre-defined time period.
      3. Average FLOAT - position of the base is calculated from a FLOAT solution over a pre-defined time period.
      4. Average FIX - position of the base is calculated from a FIX solution over a pre-defined time period. In this case, the base station needs to be connected to another NTRIP service and acts as a device.
      5. RTCM3 messages - select 10Hz
    4. Go to Base output and select the NTRIP option
    5. Configure NTRIP access credentials. If Emlid's NTRIP caster is used, use the values Emlid's NTRIP caster My mount points section; otherwise, use default values to configure the credentials. IMAGE Definition of Emlid NTRIP caster credentials.
    6. Used the credentials from Emlid's NTRIP caster's configuration.
    7. Save settings
Note: Antenna height is different from the pole height.


Emlid base station using 4G

The 4G connection type requires that Emlid's NTRIP caster can be used, which simplifies the setting procedure.

Tip: Setting up the base station with a 4G connection allows the reference point to be up to 10km of the measurement site, and the PIX4Dcatch scene can cover a larger area.
  1. Ensure that Emlid base and PIX4Dcatch have a stable internet connection via 4G on the entire site.

Emlid base station using a local WIFi network

There are two ways to use WiFi for broadcasting NTRIP corrections. The simplest way is if a WiFi network exists on the site, and the WiFi has an uplink to the global internet.

Please consider the following:

  • If there is no existing WiFi available, then a new network has to be created. Emlid's receivers can create a WiFi hotspot, please refer to Emlid's documentation. The network name will be like reach:XX:XX.
    Tip: When setting up a local network, be aware that the WiFi has stable coverage for the entire scene.
  • If there is no global uplink available, then Emlid's NTRIP caster cannot be used and a local NTRIP service has to be provided.
    Tip: The RTK base station and the RTK device have to share the same WiFi network. Please ensure that there is stable coverage at the reference point.
  1. If there is no existing Wifi network, create a local WiFi network with the Emlid's base station; by this, the receiver will act as a hotspot.
  2. If there is no uplink to the global internet, obtain the IP address of the base station. If the base station is acting as a hotspot, then it is most probably
  3. Connect PIX4Dcatch to the WiFi network. If Emlid's hotspot is used, the network name is most probably Local NTRIP.

Configure PIX4Dcatch to use the NTRIP service

Connect PIX4Dcatch to RTK device, and for NTRIP settings, use the following values:

Emlid's NTRIP caster
Local NTRIP service
IP address of the base station
See Emlid's NTRIP caster My device section.
Configuration used when setting up base Local NTRIP. Default value: reach
See Emlid's NTRIP caster My device section.
Configuration used when setting up base Local NTRIP. Default value: emlidreach
See Emlid's NTRIP caster My device section.
Configuration used when setting up base Local NTRIP. Default value: REACH
NTRIP Coordinate Reference System (CRS)
Always WGS84 for Emlid
Always WGS84 for Emlid

Use these values to set the NTRIP connection for Catch as indicated here: https://support.pix4d.com/hc/en-us/articles/4413617714065-How-to-use-coordinate-reference-systems-in-PIX4Dcatch