General Questions Related with Workflow

[beratt54]

Hello everyone,

I'm pretty new to photogrammetry, and I'd like to use it to have a 3D model of the small wind turbine blade. The blade's length is 54cm, and the relative thickness of the object is 10% for most of the blade(the highest chord value is 15cm). I have 338 pictures at seven different height levels, taken in .raw format and converted to .tiff and f/11, ISO 200 and shutter speed 2s with a 35mm lens.

I aligned the pictures in medium quality and finished the whole workflow to create masks from the model, however, I realized from 2-3 of the masks that there were some misalignments. I have markers on the blade, so I created another model with markers, in this case, I had better alignment but not as much as I expected. There are still some slight issues with the masks. Should I try markers a couple of times to fix the issue, or is there another way to have better alignment, like calibrating the lens and using optimize cameras?

Also, markers with blue flags are automatically placed in pictures, even though they are located on the backside of the object. Should I keep them or ignore them since they can't be seen from the angle?

The last question is confidence level on the dense cloud is reaching 100. However, in the mesh model, I have 5% confidence highest. What do I do wrong?

Thank you.

Best Regards.

[Vladimir Denisov]

Hi beratt54
Remove all blured images, align all wrong placed markers (also blue) and make new alignment in high quality.
If blue markers placed in wront places, then some images not aligned properly.
Some screenshots is needed to understand whats wrong in your case.

[beratt54]

Hello Vladimir,

Hi beratt54
Remove all blured images, align all wrong placed markers (also blue) and make new alignment in high quality.
If blue markers placed in wront places, then some images not aligned properly.
Some screenshots is needed to understand whats wrong in your case.

I will try your suggestions and update you here tomorrow. If you can tell me which screenshots(or at what process) you need, I can provide them as well. Thank you for your reply.

Best.

[Vladimir Denisov]

beratt54 try to make 3d mesh witout textures (based on depth maps, not desnse cloud), and show result.

[beratt54]

beratt54 try to make 3d mesh witout textures (based on depth maps, not desnse cloud), and show result.

Hello Valdimir,

Sorry for the late reply. I had to deal with the 'assertion failed' issue, but I solved it by increasing the key points. I attached screenshots from marking, dense point cloud confidence and mesh confidence(created by depth maps). After applying your suggestions, I had really nice masking so the alignment should be fine. In the screenshot from marking process, point 6 (blue flag) is placed behind the object so I unmarked it, it should be like that, right?

I also realize that after I applied optimize cameras(I calibrated lens via my PC screen with chessboard with 6 pictures), my reprojection error is increased. I think that should normally decrease, do you think is there any issue with calibration process? I applied the optimize cameras after I upload calibration file and checked the fit additional corrections.

Thank you.

Best Regards.

[Vladimir Denisov]

Try to shoot photos with the aperture as closed as possible to get the sharpest shots with the most detail (you need a lot of light for this, you can shoot outdoors, but in the shade.). This will give more detail and more feature points and less chance of error.
For shooting such a small object, you can hang it on a string and rotate it while shooting, and shoot from one position.

To shoot uniformly colored objects, you can use the following technique - splash the object of shooting with colored water from under water paints and dry it. This will give a unique texture and the accuracy will be very high. The paint can then be washed off.