Mission over lapping and large area topography

PIX4Dcapture
1

Hi all,

I am new working with Pix4 d and a have few question.

I have a large area project to acquire information and generate a topography and export the contours to auto cad . In order to cover the whole project, I need to make over 10 mission in the same project ,I will use GCP all around the project and the drone can fly from 30m up to 60 m.

Any recommendation about GSD, elevation or other please advise but here is my main question:

  1. How I make sure that every mission will have a over lap?

  2. There is max photo that can be process in mapper ?

  3. Is necessary that the GCP on every mission? If so one or more than one ? ( this question is because, I will use GCP but it may not be in all mission grid)

  4. To get accuracy is important the GSD up to what GSD is save for a excelente result.

Thanks and any input it will be appreciated.

2

Hi,

As you said, the GSD has a direct influence on the accuracy of the results. The best is that you check the project requirements and then adjust the GSD accordingly.

Keep in mind that flying lower greatly increases the amount of image and you might not be able to process all of them at once in Pix4Dmapper. It is worth considering increasing the GSD a bit in order to acquire fewer images.

To answer your questions:

  1. Make sure that each plan captures the images with enough overlap.
  2. The maximum number of images depends on the image resolution, image content, available hardware…. We typically say that processing more than 5000 in a project can present a challenge and you could run out of hardware resources.
  3. We highly recommend using GCPs. Especially in the overlapping area between flights.
  4. The selected GSD depends on the required final accuracy. Generally speaking, we recommend flying higher when convering large areas or when flying over homogenous areas (fields, forests,…)

We developed a new software Pix4Dmatic that is optimized for large scale projects. It can process large projects in one go and there is no need to split and merge them. Feel free to have a look and try it out.

Best,

3

Thanks for the info…

I have another question:

I always use GCP but I want to add check point, how I can add this check point in Pix 4 d and make sure that the result of it will run in the quality report.

What calculation I need to make to compare the check point x y z field collected and x,y,z generate in the Pix4D and how I can report this results of this comparative. Do you have a example of this calculation and report ?

Thanks and advise

4

Checkpoints (CPs) can used to assess the absolute accuracy of the model in Pix4Dmapper. The marks of the checkpoints are used to estimate its 3D position as well as potential errors in the clicks. This way, the relative accuracy of the area of the checkpoints may improve.

The difference between the initial and the computed positions of the checkpoints is displayed in the quality report and it gives an estimation of the absolute accuracy of the model in the region.

To use checkpoint, simply change the label to Check point in the GCP/MTP manager and start the processing.

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For more information about the quality control of a project: Quality report specifications.

5

Thanks for the respond. Just to be clear. When you select check point the program only check the point do not use it for processing ?

Thanks

Juan G. Marrero Donate
Sr. Project Manager

Geomark Group, LLC
P.O. Box 732

Manati, PR. 00674

939.251.9761+ C

geomarkgroupllc@gmail.com

6

The project will not be georeferenced (shifted or scaled) based on checkpoints and the imported coordinate values of checkpoints will be compared with the calculated ones.

However, the marks (clicks on images) are used during processing and this might improve the relative accuracy of the area of the checkpoints.