How to merge projects - PIX4Dmapper

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This article provides step-by-step instructions on how to merge projects in PIX4Dmapper. There are two parts when merging a project: Before merging projects and while merging projects.

It is possible to merge projects for which step 1. Initial Processing has already been completed in PIX4Dmapper. This allows the combination of information from different projects into one single project.

Merging projects is useful when:

  • There are different image acquisition types, such as terrestrial, circular, and grid image acquisition types are used. This is very helpful when reconstructing an object which requires a terrestrial, circular, and grid images. For example, images obtained from a handheld camera and a drone can also be combined to generate detailed 3D models.
  • The dataset is considerably large for the capabilities of the available processing resources.

Merging projects can speed-up step 1. Initial Processing time. It can also be used for projects having processing issues during step 1. Initial Processing with respect to memory use (not enough memory).

Note: After merging, the subprojects do not have an impact on the merged project. They can be deleted, moved or modified.
   

Before merging projects

If a project consists of several flights, it is possible to process each one separately and then merge the several subprojects:
  • Create a new project for individual flights following: Create a project. We will call this the subproject.
    For more information on how to split a project into sub-projects: How to split a project into subprojects.
  • Process Step 1. Initial Processing for each subproject.
  • Identify and mark a minimum of three manual tie points (MTPs) that have the same name and point to the same feature on both or all the subprojects. How to add / import and mark manual tie points (MTPs) in the rayCloud. It is very important for the MTPs to have the same name at the same location in all subprojects. If the naming is not consistent throughout the subproject, it can cause processing issues. Ensure the MTPs are located where the subprojects overlap. 
  • Reoptimize each subproject after adding MTPs and save them. Menu Process > Reoptimize

If a project is too large to be processed at once due to the processing resources, it can be split into subprojects.

Important: Two or more projects can be merged only if ALL of the following conditions are fulfilled:
  • The coordinate system (both horizontal and vertical) of the images has to be the same in all subprojects. Note: A subproject with no image geolocation can be merged with a subproject with image geolocation.
  • The GCPs must be in the same coordinate system (both horizontal and vertical) in all subprojects. Note: A subproject with no GCPs can be merged with another subproject with GCPs.
    It is highly recommended the GCPs to be added in the merged project, especially when more than 2 subprojects are merged.
  • The output coordinate system (both horizontal and vertical) of all subprojects has to be the same. Note: A subproject with no georeference (arbitrary system) can be merged with a subproject with georeference.

For more information about the Image / GCP / Output Coordinate System: How to select / change the Image / GCP / Output Coordinate System.

Merging projects

1. Open PIX4Dmapper.
2. On the Menu bar, click Project > New Project..., the New Project wizard opens:
3. In Name, type a name for the merged project.
4. (Optional) In Create in: click Browse... On the Select project location pop-up, navigate to select the folder where the project and results will be stored and click Select Folder.

Note: A folder named after the project will be created in the selected folder and it will store all the results.

5. (optional) Select the check box Use As Default Project Location to save all new projects in the selected folder.
6. Selected the option Project Merged from Existing Projects.
7. Click Next.
8. On the Merge Projects page, the Duplicate camera parameters option is activated by default. If the camera model of the different projects is the same, it is duplicated by adding the name of the project at the end of the original camera model name.

Note: This option allows the user to optimize the camera model of each project separately, which can enhance the results. The camera model can be edited once the project is created. Unselecting the Duplicate camera parameters option is recommended only when the camera and the environmental conditions (temperature, etc.) were the same for all the subprojects to be merged.

9. Click Add projects...
10. On the Select Projects pop-up that opens, browse the project files. Select the projects to be merged (multiple selection is possible) and click Open.
11. Repeat step 9 and 10 to add more projects (if the processing resources can handle multiple projects)
12. Click Next.
13. Click Finish to create the merged project.
14. Automatically (no user intervention), the subprojects are combined and processed together. The final result of step 1. Initial Processing is generated.
15. Verify the Quality Report. One block should be created.
16. When the reconstruction consists of a single block, use the results to create another merged project, or start step 2. Point Cloud and Mesh and 3. DSM, Orthomosaic and Index.

Note: Each block is processed separately when processing step 1. Initial Processing before merging. When merging:
  • If at least 3 Manual Tie Points were marked in the overlapped area between the subprojects in each subproject, and if they have the same label in all subprojects, a pop-up window will appear when creating the merged project. It will ask if they are the same Manual Tie Points and have to be combined. If they are the same, then the software can join the blocks and create only one block.
  • If there are not at least 3 Manual Tie Points when merging, two or more blocks are created. Therefore, after merging the projects, it is required to add at least 3 Manual Tie Points in the overlapped area and Reoptimize in order to obtain a single block. By generating the Quality Report it is possible to verify that one block was created.

By checking the Automatic Tie Points displayed in the rayCloud it is possible to confirm the adjustment of the two projects.

Troubleshooting

It is very important that before merging, all subprojects are processed successfully and there are no issues reported in the initial checks of the quality report, e.g. bad camera optimization, uncalibrated camera, or multiple blocks.

If possible, try processing projects with similar flight height and camera orientation together as one project rather than merging. This can simplify the process of getting the sparse point cloud to align properly.

Cases where the projects fail to align properly relative to each other are due to:

  • There is not enough overlap between image acquisition plans.
    • Make sure that each plan captures the images with enough overlap.
  • Not enough matches between the subprojects.
    • Add more common Ground Control Points or Manual Tie Points in the subprojects before merging.

The workflow for merging multispectral projects is different and is described here.

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8 comments

  • reseller aerocamservicios

    Excelente explicación, de mucha utilidad en los levantamientos para catastro urbano en donde las cantidades de fotografías son enormes.

  • NV CTG

    I am trying to model a bridge. I took a series of drone shots which are georeferenced and I built a model from that. I also took non-georeferenced ground shots from a Sony camera and built a model from that. The scale on the ground shots is much smaller. 

    Do I need to scale that project before merging and/or does it have to be georeferenced as well or will the MTPs take care of referencing and scaling?

  • Kapil (Pix4D)

    Hi Tylor, 

    You don't have to scale your project, MTPs will take care of the scale. Your final scale will be the same as the project with drone shots that are georeferenced. 

    Regards,

  • City of Overland Park City of Overland Park

    Hello,

    I am having problems merging two projects and I am not sure where the issue lies.  I have merged projects before successfully so I am not sure what I am doing wrong.  My first project is nadir and my project is oblique using an IPhone.  When I merge the projects, they end up on two different planes within the merged project.  Do you know what could be causing this issue?  The projects on their own processed fine. 

    Thanks

  • Avatar
    Beata (Pix4D)

    Hi! 

    The best solution for you would be to post on our Community where you can attach the Quality Reports so we can investigate the issue. For our convenience, we would need three; nadir, oblique and merged report. We look forward to your post and the data so we can start the troubleshooting! 

    Regards

  • Land Survey

    Thanks for the guide. 

    When I merge projects, this is my workflow:

    1. Run step one for each subproject. 

    2. Mark GCPs in each subproject, and then reoptimise.

    3. Create a new project by merging the subprojects. 

    Once the project has finished building, the GCPs show as marked in the raycloud but not in the quality report. To get a geolocation accuracy number, I have to reoptimise the merged project. This takes considerable time, as the project is now large. 

    Can I skip this reoptimisation, relying on the quality reports from the subprojects or is this reoptimisation recomended?

  • Zendesk Admin Service Account

    Hello, you should not need to Reoptimize, the GCPs should be taken into account. Please create a new community topic here

    describing the problem and attaching the quality reports of the individual projects (before merging) and the quality report of the merged project (before the Reoptimization), so that we can better understand the case. Thank you.

    Edited by Zendesk Admin Service Account
  • Ruben Rosland

    Thanks for the guide. 

    When I merge projects, this is my workflow:

    1. Run step one for each subproject. 

    2. Mark GCPs in each subproject, and then reoptimise.

    3. Create a new project by merging the subprojects. 

    Once the project has finished building, the GCPs show as marked in the raycloud but not in the quality report. To get a geolocation accuracy number, I have to reoptimise the merged project. This takes considerable time, as the project is now large. 

    Can I skip this reoptimisation, relying on the quality reports from the subprojects or is this reoptimisation recomended?

     

    I also had to rematch and optimize in order to get this to work.

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