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How to mark ground control points (GCPs) in PIX4Dcatch 

Users can manually mark ground control points in the PIX4Dcatch application before uploading the data to PIX4Dcloud for processing. This article describes how to mark images.

Ground control points (GCPs) are reference points with known coordinates used to accurately georeference and align photogrammetry projects. In PIX4Dcatch, images containing GCPs can be manually marked before upload. These marked images, along with the associated GCP data, can then be uploaded to PIX4Dcloud for processing.

GCPs are managed within a Point Collection, which stores the coordinate information for each point. For GCPs to be used during processing, at least three points must be marked, and each must appear in a minimum of two images.

Important: The Point Collection must be in a projected coordinate reference system.

To create Manual Ground Control Points follow these steps:

  1.  Open the Project tab file_blk.jpg .
  2. Select the project.
    projects view
  3. Tap the Tools tools icon icon.
  4. Select the GCP Marking icon GCP icon and select the Point Collection from the list. When a Point Collection is selected, the application will display a list of points from the Point Collection.
    survey list list GCP Marks
  5. When a specific GCP Mark is selected, a new screen will appear showing the images and a map. 
    GCP view

  6. Tap the image once to place the mark. For precise placement, tap and hold to open the magnifier tool. To expand the image or remove a mark, tap the three-dot menu at the top-right corner of the image.

    Menu GCP Mark GCP

  7. To ensure coverage, mark the GCP in at least two images.
  8. GCPs will appear on the map, and the images where a GCP has been marked will be highlighted in green.

    Plantilla Iphone (37)
  9. Tap Save to confirm the Marks.

  10. Select and mark any additional GCPs needed for the project.

Tip: To achieve the highest absolute accuracy, mark each GCP in as many images as possible and place the marker at the pixel level using the highest zoom level.

To process a project with GCPs, please visit Processing projects - PIX4Dcatch.