Output Coordinate Reference System - PIX4Dcatch

A coordinate reference system defines the horizontal and vertical positioning of PIX4Dcatch data. It can be selected when uploading a project to PIX4Dcloud or when creating a Point Collection. This article describes how to select the output CRS.

A coordinate reference system (CRS) defines how coordinates are represented on a map. In PIX4Dcatch, the output CRS can be selected when uploading a project to PIX4Dcloud or when creating a Point Collection.

When uploading to PIX4Dcloud, the selected output CRS defines how the reconstruction is georeferenced after processing. Both the horizontal and vertical components of the CRS can be set automatically or manually and do not need to match the original (input) geographic CRS.

When creating a Point Collection, the horizontal and vertical CRS can also be specified.

Additionally, if a project is exported and processed in PIX4Dmatic or PIX4Dmapper, the output CRS can be defined within the desktop software.

How to select a coordinate reference system when uploading to PIX4Dcloud

Navigate to the project to be uploaded. Then open the project and follow the next steps:

1. Press Upload icon.

2. Select the account and organization.

3. Select the upload location.

4. Click Next to select the processing options.

5. Tap the Output coordinates reference system.

6. Select one of the three options: Auto Detected, Known CRS, or Site Localization.

Auto Detected automatically sets the projected horizontal coordinate reference system in the UTM zone corresponding to the project's location. The vertical coordinate reference system is automatically defined as ellipsoidal height.

Known CRS is a manual selection. Only a projected horizontal coordinate reference system can be selected

If the filter is set to "recommended," only the suggested CRS for the project area is displayed at the top of the list. Conversely, if the filter is set to "all," all CRS options available worldwide are shown in alphabetical order. A warning icon indicates that the selected CRS may be far from the project's current location.

When configuring the vertical coordinate reference system, either ellipsoidal height or orthometric height can be selected:

• Ellipsoidal Height is based on a reference ellipsoid (e.g., WGS84) and does not require a geoid model.
• Orthometric Height requires a vertical coordinate reference system with an associated geoid model. If no geoid model is available, a geoid height must be manually entered.

If the appropriate vertical coordinate reference system is unknown, use ellipsoidal height.

The last selected CRS is automatically saved and is used as the default CRS in future projects. It can be changed at any time.

Site Localization requires an existing site localization to be created in advance. Additional information can be found here.

7. When the CRS is selected, tap the Upload button.

8. Once it is uploaded there will be the Cloud icon. 

How to select a coordinate reference system when creating a Point Collection

A Point Collection is the placeholder for storing or importing a single-point measurement. A single-point measurement is also known as a ground control point (GCP) and can be used to georeference a photogrammetry project.

The Point Collection can be created with a known CRS or a site localization.

To obtain better results, it is recommended to use RTK devices for centimeter accuracy.

When a point collection is created and measured using RTK, only one geographic coordinate reference system will be available—corresponding to the CRS specified when connecting to the NTRIP server. If the RTK rover is disabled, the only available coordinate reference system will be WGS84.

To create a new Point Collection follow the steps detailed here.