How to import and mark Ground Control Points(GCPs) in PIX4Dcatch


It is possible to capture and mark Ground Control Points (GCPs) in PIX4Dcatch projects. After the capture, select a point collection to start the process, allowing for PIX4Dcatch projects to achieve higher absolute accuracies that GCPs provide. 

Obtain GCP Collection

GCPs are stored in a Point Collection with corresponding coordinates.

Important: Processing will use the Collection's coordinate system for the output coordinate system. Therefore the following has to be considered during GCP measurements:
  • Projected Coordinate Reference System is required.
  • Site Localization and Geographical Coordinate Systems are not allowed.

Measure GCPs in a project

PIX4Dcatch with the RTK rover can also be used to measure and collect GCPs. For more information: How to measure single points(GCPs) - PIX4Dcatch RTK.

Tip: Add reference images of your GCPs and description to help you, later on, to mark the GCP at the correct place.

Import GCPs to PIX4Dcatch

PIX4Dcatch is also capable of importing GCP coordinates into an existing Collection. If the desired Collection does not exist yet, please create it first. Then there is an option to Import Points. Please note that coordinates have to be in the same coordinates system as the Collection itself. For input format, please refer here: Tie points (GCPs, CPs) import format - PIX4Dmatic

Mark GCPs in PIX4Dcatch

  1. file_blk.jpg Open the Project management dialog.


  2. Select the project.


  3. GCP_management.png Open the Point Collection selection dialog you want to use as GCPs.


  4. Close the dialog; the GCP icon will turn blue, selected Collection will be displayed. Now, the Mark points is also available.


  5. GCP_marking_mark_points.png Select Mark points.
  6. Select the GCP from the list to mark.


  7. Mark GCP on an image with a single tap. Hold tapping a bit longer to open the magnifier for more accurate marking. To expand an image or delete a marking, tap the 3 dots at the top right of each image.

    PIX4Dcatch_GCP_marking_magnifier.png PIX4Dcatch_GCP_marking_magnifier.png

  8. Mark the GCP at least on two images.
  9. GCPs will be shown on the map; marked images will be displayed in green on the map.
  10. Tap Save.
  11. Select and mark additional GCPs for the project as before.
Tip: For maximum absolute accuracy, mark GCPs on as many images as possible and also use the maximum magnification level to be able to mark the GCP at the pixel size level

Process projects with GCPs

There are two main ways to process data obtained with PIX4Dcatch.and also to use the maximum zoom level to be able to mark the GCP at the pixel size level

Important: Processing will consider GCP markings only if the project includes at least two marked GCPs.

Processing PIX4Dcatch projects with GCPs on PIX4Dcloud / PIX4Dcloud Advanced

The most automated way to process is to upload data from PIX4Dcatch to PIX4Dcloud. This will include marked GCPs in the project and send a notification once the processing is ready and all requested results are available.

Processing PIX4Dcatch projects with GCP marks in PIX4Dmatic

  1. Export the project files from PIX4Dcatch. How to export PIX4Dcatch projects (iOS/Android) for more information.
  2. Create a New Project in PIX4Dmatic with the data.
  3. Process locally in PIX4Dmatic and eventually upload the results to PIX4Dsurvey or PIX4Dcloud, if needed. How to import a PIX4Dmatic project into PIX4Dsurvey, or How to upload or replace results to PIX4Dcloud for more information.
    Tip: PIX4Dmatic has the ability to process PIX4Dcatch projects with LiDAR depth data using the Depth and dense fusion option, as well as having a Sky filter and Noise filter which benefits oblique imagery.


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