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Coordinate reference systems - PIX4Dcatch

This article explains how to correctly set up the NTRIP, output, and GCP coordinate reference systems to ensure accurate RTK and non-RTK georeferencing.

IN THIS ARTICLE

NTRIP coordinate reference system
Output coordinate reference system
GCP coordinate reference system

A coordinate reference system (CRS) defines how locations on the Earth are represented using coordinates by specifying the datum, coordinate axes, units, and map projection. Based on your project setup, selecting the correct input CRS and output CRS, and applying a geoid (where necessary) are mandatory.

Note: The use of EPSG codes is strongly advised to ensure the CRS is clearly identified. Relying solely on CRS names can lead to misinterpretation. The EPSG codes of the CRSs can be searched here: http://epsg.org/.

For more information: Coordinate reference systems and 2D projections.

NTRIP coordinate reference system

NTRIP (Networked Transport of RTCM via Internet Protocol) is a protocol that streams GNSS correction data via the internet from a base station to a rover, ensuring centimeter-level accuracy. When using a supported RTK device, the NTRIP CRS is either automatically defined by the NTRIP provider or requires manual setup by the user in the NTRIP settings.

Note: For captures without RTK, PIX4Dcatch automatically defaults the image CRS to WGS84 (EPSG:4326) with ellipsoidal height.

Select the NTRIP input coordinate reference system

When pairing PIX4Dcatch with a supported RTK device, an RTK profile must be created first to define the NTRIP CRS.

To create a profile, follow the next steps:

  1. On the PIX4Dcatch home screen, tap the user icon in the top-right corner.
  2. Under Settings, tap RTK Device Settings.
    image-png-Mar-10-2026-04-20-51-5515-AM
  3. Tap Create in the bottom right corner.
    Plantilla Iphone (26)-1
  4. On the New RTK Profile screen, fill in the following information:
    • Profile Name: Insert a descriptive name for the profile.
    • RTK Rover: Select the appropriate RTK Rover from the Catalog.
    • NTRIP Settings: Define the connection parameters.

  5. Provide the mandatory NTRIP Settings:

    • NTRIP Provider Details
      • Hostname / IP
      • Port Number
      • Username
      • Password

  6. Tap Validate NTRIP

  7. Select a mountpoint
    • Select a Mountpoint
    • Input Coordinate Reference System (optional if not defined automatically).
  8.  Tap Save.

      NTRIP settings

  

Important: The selected NTRIP CRS must match the CRS used by the NTRIP service to broadcast its corrections. If this information is not readily available, contact the NTRIP service provider.

    Common CRS Used by NTRIP Providers (by Region)

    NTRIP providers typically broadcast corrections in regionally standardized geodetic reference frames. The most common CRSs by region are:
     
    Country or region  CRS
    Europe ETRS 89 (EPSG:4258)
    United States NAD83 2011 (EPSG:6318)
    Japan JGD 2011 (EPSG:6668)
    Singapore SVY 21 (EPSG:4757)

    Output coordinate reference system

    The output CRS is the system used to geo-reference the reconstructed model.

    Note: When uploading an RTK-geolocated project to PIX4Dcloud, users can manually define the horizontal and vertical CRS, including the geoid, if applicable. Manual selection of the output CRS is also available when exporting the project for use in PIX4Dmatic or other third-party software.

    For more information: Output Coordinate Reference System - PIX4Dcatch.

    Select the output CRS when uploading to PIX4Dcloud.

    1. Open PIX4Dcatch and tap Projects at the bottom.

    2. Tap the project to select an output CRS.

    3. Tap Upload upload button.
      PIX4Dcatch_Upload_button

    4. Tap coordinate reference system icon Output coordinate system.
    5. Tap Auto Detected to select the output CRS.

           upload menu

    Note: The Auto Detected setting automatically assigns the horizontal CRS to the UTM zone corresponding to the project's location. Example: For a project in Lausanne, Switzerland, the system defaults to WGS84 / UTM zone 32N (EPSG:32632) for horizontal and EGM96 height (EPSG:5773) for vertical

    Manually select the output coordinate reference system:

    1. Once tapping the Auto Detected, select Known CRS. 
    2. Tap the icon projected coordinate reference system icon to select the horizontal CRS:
      • In the Horizontal coordinate reference system dialog, search or copy-paste:
        • The name of the CRS, or
        • The EPSG code of the CRS.
    3. Tap the icon altitude icon to select the vertical CRS:
      • In the Vertical coordinate reference system menu, search or copy-paste:
        • The name of the CRS, or
        • The EPSG code of the CRS.
    4. (Optional) Tap the icon globe icon to select a geoid. If the selected vertical CRS supports geoids and the geoid model is available in the PIX4D database. Select the geoid model in the drop-down list.
    5. Tap Select in the top-right corner.
    6. Tap Upload.

    For more information on vertical CRSs and geoids: How to use vertical coordinate systems and geoids - PIX4Dmatic.

    Note: For non-RTK projects, PIX4Dcatch automatically sets the output CRS to the auto-detected UTM zone (e.g., WGS84 / UTM zone 32N (EPSG:32632) horizontal, and EGM96 height (EPSG:5773) vertical for Lausanne, Switzerland).

    GCP coordinate reference system information

    When collecting ground control points (GCPs), the user must select the CRS in which the GCPs was collected.

    Note: When creating a new GCP collection, PIX4Dcatch will prefill the horizontal and vertical fields depending on the current region and configuration information.

            Menu GCP

    Important: The exact CRS used for GCP collection must be maintained and selected when importing the GCP files into PIX4Dmatic, PIX4Dmapper, or any alternative third-party processing software.