How to use coordinate systems in PIX4Dmatic

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Image coordinate system

The image coordinate system is:

  • Automatically set to WGS84 - EPSG:4326, for the horizontal image coordinate system. The vertical coordinate system is automatically defined based on the camera model of imported images:
    • WGS84 - EPSG 7030 ellipsoid for images taken with DJI Phantom 4 RTK, senseFly AeriaX, S.O.D.A., S.O.D.A. 3D, and S.O.D.A. Corridor cameras.
    • EGM96 - EPSG 5773 geoid model for all other camera models.
  • Automatically set based on the xmp tag Xmp.Camera.HorizCS and Xmp.Camera.VertCS if they are available. More in the EXIF and XMP tag information read by Pix4D article.
  • Manually selected when using the Import image geolocations and orientations... feature.

For more information, please see our Which cameras are supported in PIX4Dmatic article.

GCPs coordinate system

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

Pix4Dmatic_set_coordinate_system.jpg

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.
     
    Note: The Geoid height value is used to convert the image geolocation (WGS 84 ellipsoid or EGM96 geoid) into the desired project coordinate system.

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

Project coordinate system

 
Tip: The project coordinate system is always visible on the bottom bar: Pix4Dmatic_project_coordinate_system_bar.jpg

The horizontal and vertical coordinate system of the project is defined based on the imported image geolocation or based on selected GCPs coordinate system:

  • When GCPs coordinate system is not defined, the project coordinate system is automatically defined based on the position of the image geolocation. The corresponding UTM zone is used. The vertical coordinate system is always set to ellipsoidal heights.
     
    Example: When importing images with image geolocation in Switzerland the automatically assigned project coordinate system is:
    • Horizontal: WGS 84 / UTM zone 32N - EPSG 32632.
    • Vertical: WGS 84 - EPSG 7030 ellipsoid.
  • 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.
     
    Example: When importing images with image geolocation in Switzerland and defining the GCPs coordinate system as CH1903+ / LV 95 - EPSG 2056 with ellipsoidal heights, the project coordinate system is:
    • Horizontal: CH1903+ / LV 95 - EPSG 2056.
    • Vertical: Bessel 1841 - EPSG 7004 ellipsoid.

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. 

PIX4Dmatic_arbitraty_coordinate_system.png

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.
 
Note: The benefit of the recommended workflow [Method - A] is that there is no need to rerun the Calibrate step. The downside is that, since the position of images and GCPs are not aligned, it is not possible to get a rough position of the GCPs on image and it can consequentially take longer to locate and mark each GCP.

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.
 
Note: The benefit of the alternative workflow [Method - B] is that the project is first georeferenced based on a small amount of GCPs. This way images and GCPs are roughly aligned, and it is easier to detect and mark additional GCPs.
By first calibrating the project, the Run AutoGCP algorithm is enabled which can additionally speed up the marking of GCPs.

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.

 
Information: Please contact support if you have additional questions regarding horizontal grid corrections and transformations or if you believe that the transformation you need is not included or precise enough.
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