Merging different GSD projects from the same zone

PIX4Dmapper PIX4Dmapper Questions/Troubleshooting
1

Hi;

If I have the next situation: Large project area with a zone covered by high vegetation, and because of that vegetation area I decide to divide my project in 2 missions. The other areas around the large forest with a GSD of 5cm/px resolution and the covered area with a 10 GSD resolution to get better results according other users recomendations.

My question is if I want them to be in the same data later, how do I merge them? Can I process them at the same time loading all of the images under the same folder in pix4d? In this case I assume my ortomosaic should have different area resolutions in the same output.

 

Best Regards

 

2

Hey Victor,
You can merge your separate projects into one project after the Initial processing step is done. I have never merged two projects that had different GSD’s so I am not entirely sure what would happen but I am guessing you may have to downsample your 5 cm GSD project into 10 cm GSD to match them. Otherwise Pix4D may not be able to stitch images that have different GSD’s.

3

Hi Selim, thanks for the reply, I was trying to figure out a way to merge the projects without sacrifying my resolution of the areas that doesn’t have high vegetation density, because honestly I don’t mind very much the resolution of the trees in the forest area. I am just thinking all the possibles scenarios to achive the best possible result.

4

Hey Victor, 

Yeah I am not sure how you can merge your projects and keep different GSD’s in a merged project.

5

Hi Victor and Selim, 

Both ways should work: 

  • process all images in the same project
  • process them separately and merge after processing step 1 (as Selim recommended): Merging Projects

As you said, each region will have a different Ground Sampling Distance (GSD). However, you should know that the GSD defined in a project is the “average GSD”. This means that if one area has 5cm/pixel and another 10cm/pixel, you will probably end up between those values for the average GSD of the project. This will have an impact on the creation of outputs such as the orthomosaic, as this one is either defined as a multiple of the average GSD or as a custom value: 

If you would select a custom value of 5cm/pixel then the area that has this GSD in the project should be fine, but the area that originally had 10cm/pixel will have sampled values, but based on your requirements this seems to be ok for you. 

Otherwise, you could process each subproject separately and try merging the orthomosaic outputs in a third party software, so that you have the average GSD for each subproject and not the same value for the entire area.

Hope this helps! Let us know what you decide to do in the end! 

6

Hi Pierangelo;

Thanks for the reply and the great observations you made. It’s very interesting this options you are talking about. I think the final decision will be based too in the other output request by client. Usually the most important output in road design are the contourn lines based on the DTM. 

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