How to use coordinate reference systems in PIX4Dcatch

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, the correct selection of input CRS, output CRS, and the application of a geoid (where necessary) are mandatory.

IN THIS ARTICLE

NTRIP coordinate reference system
Select the NTRIP coordinate reference system using the Pix4D supported RTK device
Output coordinate reference system
Select the output coordinate reference system when uploading to PIX4Dcloud
GCP coordinate reference system information

Note: For clear and unambiguous identification of a CRS, the use of EPSG codes is strongly advised. Relying on CRS names alone can be ambiguous and may lead to misinterpretation. Required CRSs can be searched for and verified at http://epsg.org/.

For a comprehensive understanding, refer to the resource: 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 over the internet from a base station to a rover, enabling centimeter-level positioning accuracy. When using a supported RTK device, the NTRIP coordinate reference system (CRS) is defined either automatically by the device’s vendor application or manually by the user in the NTRIP settings.

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

Select the NTRIP coordinate reference system using a Pix4D supported RTK device

When a supported RTK device is used for capture, it is necessary to create an RTK device profile that defines the NTRIP coordinate reference system.

To create a profile, follow the next steps:

Navigate to the main menu and select RTK Device Settings.

2. Select Create a profile

3. On the New RTK Profile screen, complete the next fields:

- 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.

4. Provide the mandatory NTRIP Settings:

- NTRIP provider details

- Hostname / IP

- Port Number
- Username
- Password

- - Mountpoint:
  - Input Coordinate Reference System:

5. Once the connection is established, select the required mountpoint under Choose mountpoint.

6. Tap the icon to select the NTRIP coordinate reference system.

7. Tap Save.

Important: The selected NTRIP Coordinate System must precisely match the CRS used by the NTRIP service to broadcast its corrections. If this information is not readily available, it will be necessary to contact the NTRIP service provider.

Common Coordinate Reference Systems 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	Coordinate reference system
Europe	ETRS 89 (EPSG:4258)
United States	NAD83(2011) (EPSG:6318)
Japan	(EPSG:6668)
Singapore	(EPSG:4757)

Output coordinate reference system

The output coordinate reference system is the system used to geo-reference the reconstructed model following processing. It is not required to be identical to the input CRS.

Note: When uploading an RTK-geolocated project to PIX4Dcloud, users are permitted to manually define the horizontal and vertical CRSs, 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 detailed information about the Output Coordinate Reference System in PIX4DCatch.

Select the output coordinate reference system when uploading to PIX4Dcloud with a RTK-enabled device.

1. Tap Upload

2. Tap Output coordinate system.

3. Tap Manual to select the horizontal and vertical coordinate reference system.

Note: 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

Manual selection the output coordinate reference system:

Tap the icon to select the horizontal coordinate reference system:
- In the Horizontal coordinate reference system dialog, search or copy-paste:
  - The name, or
  - The EPSG code of the coordinate system.
Tap the icon to select the vertical coordinate reference system:
- In the Vertical coordinate reference system dialog, search or copy-paste:
  - The name, or
  - The EPSG code of the coordinate system.
(Optional) Tap the icon to select a geoid. If the selected vertical coordinate system supports geoids and the geoid model is available in the PIX4D database, select the geoid model in the drop-down list.
Tap Done.

Important: Ensure the correct vertical coordinate system and/or geoid is selected.

Tap Upload.

For advanced information on vertical CRSs and geoids, refer to How to use vertical coordinate systems and geoids - PIX4Dmatic for more detailed information.

Note: For non-RTK projects, PIX4Dcatch automatically sets the output CRS to the autodetected 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 will be exported.

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

With a Pix4D-supported RTK device:
- Horizontal: Depends on the NTRIP CRS entered. e.g. ETRS89 (EPSG:4258), NAD83(2011) (EPSG:6318), JGD2011 (EPSG:6668), etc.
- Vertical: Ellipsoidal height
With integrated GPS:
- Horizontal: WGS 84 (EPSG:4326)
- Vertical: EGM 96

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.

For detailed import instructions, refer to How to import GCPs to PIX4Dmatic.