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Author Topic: Alignment Problem in Z  (Read 151 times)

Broken Arm

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Alignment Problem in Z
« on: May 23, 2020, 04:17:17 PM »
Hello,

I would need information because I notice a Z offset when aligning the images in the partial cloud of my project.


We had to survey with a phantom 4 RTK and its base an area of ​​30 hectares. We divided this area into several sectors that we took pictures of over several days and over two weeks.

There were no changes to flight parameters. Once the shots were finished, I imported all the images into a single chunk and started aligning the photos. I have no errors of recoveries however I note a shift in Z of certain zones as you will be able to see it on the attachments. How can I fix it? Because I then have to make a DEM and an Orthomosaic. Thanks for your help.
« Last Edit: May 23, 2020, 04:38:58 PM by Broken Arm »

Alexey Pasumansky

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Re: Alignment Problem in Z
« Reply #1 on: May 24, 2020, 09:13:17 PM »
Hello Broken Arm,

Do you have all images in the same camera calibration group in Tools Menu -> Camera Calibration dialog?
Which camera accuracy settings you are using and which optimization options you are using?

I could assume that there are almost no valid tie points between the images from the separate flights, which could be a result of different weather/light conditions or changes in the actual scene.

What I can recommend is to split the calibration groups, just for case, in the Camera calibration dialog according to each flight (at least one group per different day) and re-align the set, if you see that there is bug number of invalid tie points for the image pairs from the different flights.

Best regards,
Alexey Pasumansky,
AgiSoft LLC

Broken Arm

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Re: Alignment Problem in Z
« Reply #2 on: May 24, 2020, 09:42:14 PM »
Good evening,

I think I have found the solution which corresponds to your suggestion. I separated the shots into several chunks then I optimized the position of the cameras of each chunk which has the effect of reducing the position error to less than 1 centimeter then I make an alignment of the chunks. The result is there I no longer have the Z offset. I don't know if I used the best process. What do you think?

PROBERT1968

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Re: Alignment Problem in Z
« Reply #3 on: May 25, 2020, 06:42:10 PM »
It might be a good thing for you to screenshot what Alexey was telling you.. the Camera Calibration dialog ?

That might help what was going on ...

Alexey Pasumansky

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Re: Alignment Problem in Z
« Reply #4 on: May 28, 2020, 01:30:31 AM »
Hello Broken Arm,

If it would be easier for you to follow, I can suggest the following steps:
- add each flight images to the separate chunks,
- merge chunks (without processing anything),
- switch to the merged chunk and process the data there.

In this case all the calibration groups will be already separated according to each flight.
Best regards,
Alexey Pasumansky,
AgiSoft LLC

Broken Arm

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Re: Alignment Problem in Z
« Reply #5 on: May 28, 2020, 12:53:26 PM »
Hello everyone and sorry for my late reply. Thank you also for your advice. As I was pressed for time, I deleted the GPS data from the photos and then aligned them and it worked very well. Then, I put my control points on the ground and then I entered the GPS coordinates of the control points on the ground that a geometer sent me. And everything ended well as you can see. I will come back to see you as soon as I finish to understand with you the problem that happened. I think the problem came from the RTK mobile base of phantom 4. It was on its way but not connected to the network. I think the GPS data was not good. This is an assumption because the recovery of the photos was very good and I had no misalignment however it was the Z position which was not even on two consecutive drone flights and on the same place. bye

jwallace

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Re: Alignment Problem in Z
« Reply #6 on: May 28, 2020, 12:56:08 PM »
Awesome work