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  • Geo-reference your model in minutes: ground control point (GCP) orientation

Geo-reference your model in minutes: ground control point (GCP) orientation

Geo-reference your model in minutes: ground control point (GCP) orientation

Geo-reference Your Model in Minutes: Ground Control Points Orientation

When it comes to geospatial data analysis, achieving survey-grade accuracy is critical. Even minor errors can have significant consequences, leading to inaccurate conclusions and wasted resources. Ground Control Points (GCPs) provide an effective solution, enabling high-precision geo-referencing for your models in 3Dsurvey. GCPs improve both absolute geospatial positioning and ensure correct scale and orientation of your model. 

3Dsurvey can process images without geolocation. When images have no geolocation, 3Dsurvey uses additional information to locate, scale and orient the model correctly. Ground Control Points (GCP) will both improve your absolute geospatial orientation and place the model at the correct location, scale and orientation.

Need more information? Watch GCP Orientation Troubleshooting tutorial!

Watch the Tutorial

How to Orient a Model with Ground Control Points

To orient your model with GCPs, we start with a model resulting from a bundle adjustment, which may lack proper scale and orientation if no telemetry data is available.

  1. Begin Orientation with GCPs:

    • Click the “Orientate” button and select “Orientate with GCPs.”
    • Browse to select a .txt file containing GCP positions. This file should include point IDs, along with X, Y, and Z coordinates.
    • Specify the coordinate system if required, or opt for a local coordinate system to avoid transformation.
  2. Mark Approximate GCP Positions:

    • Identify at least three approximate GCP locations in the model. You can zoom in or out using the mouse wheel to locate points.
    • Select the point ID on the minimap, then left-click the GCP’s approximate position in the image.
    • To clear a point, click “Clear mark,” or use “Clear all marks” to remove all GCP positions from all images.
    • If unsure of point IDs, simply right-click on a GCP in the image to mark it as unknown. The software will attempt to auto-detect based on geometry once three points are marked.
  3. Refine and Confirm GCP Positions:

    • After confirming the initial positions, navigate through the images to refine GCP locations as needed.
    • Right-clicking the GCP’s actual location allows you to refine the position further.
    • Once positions are refined, click “Next” to proceed.
  4. Measure and Adjust GCP Positions:

    • The software displays all GCP positions across images. You can zoom in and manually adjust as necessary.
    • Double-clicking enables or disables individual point measurements.
    • After confirming all GCP positions, proceed by clicking “Next” for the software to adjust the model.
  5. Assess and Validate GCP Errors:

    • The GCP error screen displays the difference between imported GCP positions and photogrammetrically derived positions. This serves as an accuracy check.
    • For an independent validation, return to the GCP list, change a few GCPs to “Validation” points, then proceed. Validation points serve as a separate accuracy check, ensuring precision typically within 3 cm.
  6. Finalize Model Orientation:

    • Upon finishing, your model will be correctly oriented and scaled. The positions of cameras, GCPs, and validation points will also be displayed in 3D.

With these steps completed, your model is now ready for dense reconstruction, offering high accuracy for your geospatial projects.

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