This article explains how to include GCPs on PIX4Dcloud Advanced for their automatic detection.
IN THIS ARTICLE
For the AutoGCPs detection algorithm to be successful, the following requirements regarding the images and the GCPs have to be met. Additional information and best practices are available at Automatic detection of targets - AutoGCP algorithm.
- 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.
- Squared, diagonal and Aeropoints targets are supported.
- The recommended size is 20 times the average GSD of the project.
- 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 whose definition is included at https://epsg.io.
- 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.
Once the CSV file is uploaded, specify the additional properties for the GCPs.
- Coordinate system: Drag and drop or browse the .prj file with the coordinate system definition (preferred) or use the search functionality by clicking I don't have a PRJ file. More information about coordinate system files in How to select the GCP coordinate system when working in the Cloud.
- Diagonal target size: Specify the diagonal length of the targets in centimeters or inches.
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 its properties.
- Ensure that the imported coordinates are correct
- (Optional) Change the Type of the control points by opening the dropdown menu and select GCP or Checkpoint
- (Optional) If the values are inverted, easily swap Easting with Northing coordinates, by opening the dropdown menu available when clicking one of the two words in the table header.
Control points Map
By 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.
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. In case 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 GCPs were detected by the algorithm, the details of the GCP marks will be shown.
An AutoGCP report (PDF) is also generated and available for download. This report shows the detected marks for each point and it is intended to be used to ensure the GCPs have been correctly marked automatically. More information on how to download this report in How to download results from PIX4Dcloud.
An example of report for AutoGCPs marking follows.