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Author Topic: Axis issues from DJI P4 images  (Read 860 times)

ecp

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Axis issues from DJI P4 images
« on: October 12, 2020, 04:39:18 PM »
So I know this is not a new issue, and I've really tried digging into previous forums (e.g. https://www.agisoft.com/forum/index.php?topic=4986.msg38769#msg38769, https://www.agisoft.com/forum/index.php?topic=12475.msg55437#msg55437, https://www.agisoft.com/forum/index.php?topic=5739.msg27997#msg27997, ) but I can't seem to remedy my issue. Admittedly I'm very new to Metashape so I'm hoping the fix is obvious to someone a bit more experienced.

The following issue is one that I'm having, to varying degrees, with the 15+ models I'm trying to create (note: I'm not using GCPs). The axes as they manifest from the EXIF data are not correct or even realistic (screenshot 1).

My workflow is to:
1- Load images
2- Remove EXIF info
2.5- Apply masks
3- Align images to build sparse cloud
4- Select and delete "bad dots" then "optimize" --> Rinse and repeat until it looks good
5- Build dense cloud
6- Delete bad dots
7- Create mesh
8- Decimate mesh (to 1,000,000 faces to keep file size shareable, leave larger if only planning to use in Metashape)
9- Generate texture
10- Add back the EXIF data from images
11- "Clear" the cameras with large errors & rerun the location calibration <-- not sure how to do this one... might be my issue...?

This workflow was suggested to me by another user. I've attached a second image (screenshot 2) of what the model should roughly look like in its natural orientation, but you'll note the axes are mismatched in this image (Z should be Y, X should be Z and Y should be X). A secondary question, would be: is this workflow even appropriate/optimal for data without GCPs?

Finally, I've incorporated a picture of the first several rows of my reference pain for EXIF data (screenshot 3).

I've double checked the altitudes in the RAW EXIF from the images and they seem to be accurately represented in Metashape so don't think its the DJI altitude issue referenced here (https://agisoft.freshdesk.com/support/solutions/articles/31000152491-working-with-dji-photos-altitude-problem-. I've also played with changing the coordinate system in the reference settings to no avail.

Any help would be greatly appreciated.

System specs: (screenshot 4).

-Ethan
« Last Edit: October 12, 2020, 04:41:16 PM by ecp »

Alexey Pasumansky

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Re: Axis issues from DJI P4 images
« Reply #1 on: October 13, 2020, 01:14:28 AM »
Hello Ethan,

X axis is for Longitude, Y - for Latitude and Z - for altitude. Are you observing a differnet behavior in your project?

If you do not care about real world scale of your model you can perform the following steps in the beginning of your workflow after loading images:
- select all cameras in the Reference pane and use Clear option from the context menu after right-clicking on selection,
- switch the coordinate system in the Reference pane settings dialog to Local Coordinates,
- right click on the chunk's label in the Workspace pane and use Reset Transform option.
Process the data as usual then and after you've go the model use Rotate Object tool in order to defined the orientation of the model according to your needs in the Model view mode.
Best regards,
Alexey Pasumansky,
Agisoft LLC

ecp

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Re: Axis issues from DJI P4 images
« Reply #2 on: October 15, 2020, 01:06:32 AM »
Hi Alexey,

Thanks for the helpful information! I assume that means that the X axis should be parallel to longitude, etc.?

Regardless, that certainly clarifies that a few of my models seem to be ok, but I still have issues in others with the axes not reflecting reality. I've attached another pic where I've tried to orient the model to be a top-down view. Accordingly the Z axis should be in line with the view, but you'll note that it isn't. Unfortunately I am interested in the real-world scale as I'm hoping to measure aspects of the models (assuming I can trust them).

-Ethan

ecp

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Re: Axis issues from DJI P4 images
« Reply #3 on: October 15, 2020, 01:14:59 AM »
Hi Alexey,

Thanks for the helpful information! I assume that means that the X axis should be parallel to longitude, etc.?

Regardless, that certainly clarifies that a few of my models seem to be ok, but I still have issues in others with the axes not reflecting reality. I've attached another pic where I've tried to orient the model to be a top-down view. Accordingly the Z axis should be in line with the view, but you'll note that it isn't. Unfortunately I am interested in the real-world scale as I'm hoping to measure aspects of the models (assuming I can trust them).

-Ethan


Alexey,

I think I figured it out. I had been playing with reference coordinate systems to try and figure things out before. Now that I know that XY and Z are Long, lat and Alt, though,  I think the models that still have issues are the ones that I messed around with different coordinate systems with. Thanks for your help!