**IN THIS ARTICLE**

Image coordinate system

GCPs coordinate system

Project coordinate system

Arbitrary coordinate system

Horizontal grid corrections and transformations

## Image coordinate system

PIX4Dmatic allows the image coordinate system to be manually set or edited.

To edit the image horizontal or vertical coordinate systems, click on the edit icon in the lower right corner of the screen where the camera model is displayed.

How to open the image coordinate reference system picker in PIX4Dmatic.

After clicking on the edit icon, the Set image coordinate reference system (CRS) dialog box will open.

PIX4Dmatic image coordinate reference system picker dialogue box.

Unless a camera is in the PIX4Dmatic camera database or the images have the correct xmp tags, the default image coordinate system is WGS84 (EPSG: 4326) for the horizontal and EGM96 (EPSG: 5773) for the vertical.

## GCPs coordinate system

Both the horizontal coordinate system and the vertical coordinate system can be defined in the *Tie Points* table:

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.

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)
*Geoid:*If the selected vertical coordinate system supports geoids and the geoid model is available in the PIX4Dmatic database, select the geoid model in the drop-down list. - (Optional)
*Geoid height:*If the selected vertical coordinate system supports geoids but the geoid model is not available in the PIX4Dmatic database, enter the value of the geoid height at that location.

For more information and the list of supported geoids, please see How to use Geoids in PIX4Dmatic.

## Project coordinate system

The horizontal and vertical coordinate reference systems of the project are defined based on the imported image geolocation data or the selected GCPs coordinate reference system:

The project coordinate system is always visible on the bottom bar:- When the
**GCPs coordinate system is not defined**, PIX4Dmatic will default the project coordinate system to the corresponding**UTM zone**based on the position of the image geolocation. The vertical coordinate system is set to**ellipsoidal heights*.**

- When
**GCPs coordinate system is defined**, the**project coordinate system corresponds to the GCPs coordinate systems**. If the GCPs coordinate system is geographic the corresponding UTM zone is used for the project coordinate system.

## Arbitrary coordinate system

Arbitrary or local coordinate systems are typically used in constructions sites, or in mining. The origin of the system is based on arbitrary (local) points and is not aligned with any known coordinate system.

In PIX4Dmatic, Ground Control Points (GCPs) with arbitrary coordinates can be used to georeference the project in an arbitrary coordinate system.

Select the *Arbitrary CRS* and units (*m, ft, ftUS*) of the GCPs.

The recommended workflow [**Method - A**] is to:

- Create a project and import images.
- In the
*Select the GCP coordinate reference system (CRS)*, click**Arbitrary CRS**and select the units. - Import the GCPs.
- Mark GCPs on images.
- Run
*Calibrate*step.

The alternative workflow [**Method - B**] is to:

- Create a project and import images.
- In the
*Select the GCP coordinate reference system (CRS)*, click**Arbitrary CRS**and select the units. - Run
*Calibrate*step. - Mark at least 3 MTPs in the exact area where the GCPs appear.
- In the
*Tie Points*table, change the type of marked MTP to GCPs and manually insert their coordinates. - Rename the MTPs to the actual name of the GCP in the import file.
- Rerun the
*Calibrate*step by selecting the*Reoptimize cameras.* - Import and mark additional GCPs.
- Rerun the
*Calibrate*step by selecting the*Reoptimize cameras.*

## Horizontal grid corrections and transformations

PIX4Dmatic supports the most common horizontal grid corrections and transformations.

The corrections will be used automatically based on the selected coordinate systems.

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