Vertical Shift between the Model and the GCPs / Cannot mark the GCPs in the rayCloud

Error

The rayCloud displays the Ground Control Points (GCPs), in blue, far above or below the model. The GCPs do not align with the images and the model.


Description

After running step 1. Initial Processing and importing the GCP coordinates, no thumbnail is displayed in the right sidebar when clicking a GCP. The vertical shift between the images (wrong location) and the GCPs (correct location) is too significant for the points to be linked to the model. Therefore, the software cannot estimate the projection of the points on the images where the image marks are supposed to be. As a consequence, the marking is not possible in the rayCloud.


Cause

The elevation of the images written in the EXIF data (geotags) are measured by the drone's GPS. These coordinates may be inaccurate and depending on the drone and the project's location. The inaccurate elevation measurements can result in a vertical shift that exceeds 100 meters. To address the error the project must include GCPs. Follow the procedure below to use the rayCloud to incorporate GCPs.

 
Note: The error introduced by the inaccurate elevation measurements collected by the drone's GPS only introduces a vertical offset, meaning that project's relative accuracy is not affected. 

Once the project is created and the images are imported:

1. Process step 1. Initial Processing.
2. Create at three new Manual Tie Points (MTPs) using the right sidebar of the rayCloud. Each new MTP must correspond to a GCP landmark or feature that is visible in the image content. These MTPs will be converted to GCPs later. For more information: 202560109.

 
Important: For each MTP:
  • In the Label field, write the name of the GCP and make sure it is identical to the GCP name stored in the GCP coordinate file.
  • Do NOT edit or manually enter the GCP coordinates.

3. Import the GCP coordinates using the GCP/MTP Manager. For more information: 202560039.
4. Click Yes to All, so that the MTPs are converted to GCPs and the coordinate values are overwritten with the correct values.


5. On the Menu bar, click Process > Reoptimize. The model should adjust to the three GCPs.
6. Mark the other GCPs (if any) in the rayCloud following: 202560769.

 

 

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