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 way above or below the model. The GCPs do not align with the images and the model.


Description

After running step 1. Initial Processing and inserting the GCPs, no thumbnail is displayed in the right sidebar when clicking a point. The vertical shift between the images (wrong location) and the GCPs (accurate location) is too significant so that it prevents the points from being linked to the model. Therefore, the software cannot estimate the projection of the points on the images where the ground marks are supposed to be. As a consequence, the marking is impossible in the rayCloud.


Cause

Images' vertical coordinates written in the EXIF (geotags) are measured by the drone's geolocation equipment. These coordinates could be inaccurate for some drones and depending on the location of the area that is mapped.The resulting vertical shift can reach an error of 100 meters. As a consequence, it is recommend to process the project with GCPs to fix these uncertainties and to follow the procedure below to use the rayCloud for marking the points.

 
Note: It is just a vertical offset meaning that inside the model the accuracy is not affected, only the geolocation is.
 


Solution

 
Tip: If no GCPs were measured on the field, it is possible to get for instance 3 points from a Web Map Service server (e.g. Daft Logic): 202560149. The Daft Logic website takes the coordinates from Google Maps that are measured according to WGS 84 and egm96 for the Mean Sea Level (MSL) vertical reference.

Once the project is created and the images are imported:

1. Run step 1. Initial Processing.
2. Select the appropriate coordinate system of the GCPs. For more information: 202560029.
3. Create 3 Ground Control Points (GCPs) manually using the right sidebar of the rayCloud. The mark of these GCPs should correspond that of GCPs that are intended to be imported later. For more information: 202560109.

 
Important: For each point that is manually added:
  • In the Label field, write the name of the GCP and make sure it is the SAME as the one written in the input GCP file containing the coordinates.
  • In the Type field, select 3D GCP or 2D GCP from the drop-down list.
  • Do NOT edit or enter the point coordinates.

4. Import the GCP coordinates into the project from the file using the GCP/MTP Manager. For more information: 202560039.
5. Just after importing the points, a window pops up. Click Yes to All, so that the previous coordinates of the 3 GCPs that were created are replaced with the information contained in the input file.



6. On the Menu bar, click Process > Reoptimize. The model should adjust to the 3 GCPs.
7. Mark the other GCPs (if any) in the rayCloud following: 202560769.

 

 

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