AutoGCPs detection functionality - PIX4Dcloud Advanced

This article explains how to include GCPs on PIX4Dcloud Advanced for automatic detection.

IN THIS ARTICLE

Image and GCP requirements
Upload the GCP file
Define the GCP coordinate system
See and edit the defined control points
Start processing
AutoGCP report

Access: This feature is only available on PIX4Dcloud Advanced and when a 3D map or a 2D orthomosaic template is selected.

Image and GCP requirements

For the AutoGCPs detection algorithm to succeed, the following requirements regarding the images and the GCPs must be met. Additional information and best practices are available in Automatic detection of targets - AutoGCP algorithm.

Image requirements

Image quality has to be good (blurry or low-contrast images make the algorithm fail).
Images have to be geolocated (5-10 m accuracy is enough) in WGS84 (EPSG:4326).
Images have to be taken at nadir or slightly oblique angles.

GCP requirements

Squared, diagonal, and Aeropoints targets are supported.
The recommended size is a minimum of 20 times the average GSD of the project.

Example: If the average GSD of the projects is 2.5 cm (1 inch), the recommended target size is 50 cm (20 inches).
Black and white targets are supported. Other colors may work in some circumstances.
GCPs must be placed at a distance of at least 10 m from each other.
GCPs must have a projected coordinate system.

Warning: If the AutoGCPs detection algorithm fails, the processing will run with no GCPs.

Upload the GCP file

Follow the instructions to create a new dataset.
Once at step 4. GCPs automation, select Upload file.
Browse the CSV file which contains the GCPs' details and click Open.
The GCPs are imported.
(Optional) Click Replace file to upload a new GCP file.
(Optional) Click to delete the GCP file.

Important: The format of the file is described here.

First column (required): Label.
Second column (not required): Type (either GCP or CHECKPOINT with capital letters). The default value is GCP.
Third column (required): X coordinate.
Fourth column (required): Y coordinate.
Fifth column (required): Z coordinate.
Sixth column (not required): XY accuracy.
Seventh column (required if the sixth column is defined): Z accuracy.

Commas should separate fields, and there should be no header. See the following example.

Example: File with 5 GCPs and 1 Checkpoint in projected coordinates without accuracy values.

001_,GCP,4392829.089,5386534.037,424.524
002_,GCP,4392772.823,5386545.0894,424.582
003_,GCP,4392732.981,5386516.197,424.723
004_,CHECKPOINT,4392761.505,5386468.789,422.646
005_,GCP,4392755.707,5386431.546,426.298
006_,GCP,4392832.252,5386456.906,427.001

Define the GCP coordinate system

Once the CSV file is uploaded, specify the additional properties for the GCPs.

Coordinate system: Drag and drop a PRJ file defining the coordinate system, or search a coordinate system based on: EPSG code or name of the coordinate system. More information about coordinate system files in How to select the GCP coordinate system when working in the Cloud.

Important: Only projected coordinate systems can be selected. If the GCPs are given in feet, the .prj file which defines the coordinate system must also be given in feet.

Warning: The output coordinate system and the GCPs coordinate system must be the same. If the user selects a different coordinate system for the GCPs, the previously defined output coordinate system will be overwritten.

Importing GCPs on PIX4Dcloud Advanced project.

See and edit the defined control points

Click See and edit control points to access the control points Table.

Control points Table

The Control points Table lists the imported control points and their properties.

Ensure that the imported coordinates are correct.
(Optional) Change the Type of the control points by opening the dropdown menu and selecting GCP or Checkpoint.
(Optional) If the values are inverted, easily swap Easting with Northing coordinates by opening the dropdown menu when clicking one of the two words in the table header.

Changing the Type of the control points from CGP to Checkpoint.

Control points Map

When clicking Map, an OpenLayers map is displayed with the GCPs and Checkpoints.

Ensure that the control points are displayed at the expected locations. If this is not the case, the coordinate system and/or values have been incorrectly defined.

(Optional) Click on a point to switch from GCP to CP or the other way around.
(Optional) Click Save to save the changes.

Start processing

Click Process to conclude the dataset creation and to start uploading the input files for processing.

The dataset starts to be processed.
The AutoGCPs detection algorithm will run. If the GCPs are not found, an email is sent to the user email address explaining that no GCPs were found and the processing will be done without using them.
When the process is finished, an email is sent and the Quality Report of the project is attached.
In the Files > GCPs section of the project, if the algorithm detected the GCPs, the details of the GCP marks will be shown.

AutoGCP report

An AutoGCP report (PDF) is also generated and available for download. This report shows the detected marks for each point and is intended to be used to ensure the GCPs have been correctly marked automatically. More information on downloading this report in How to download results from PIX4Dcloud.