Setting Group by Exif to True caused me a lot of problems...

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  • Avatar
    Götz Echtenacher

    Hi Mike,

    I am pretty certain that exif grouping does not make use of the lens data than any other alignment. It's a starting point in any case and in most cases RC can get the result even wothout the data.

    Exif grouping simply means that all cameras with the same focal length will be undistorted according to the same parameters, which are an average of all images in the group. If you have a fixes lens and don't change any settings like focus or aperture, then you should get the same or better results with grouping. On the other hand, if you change the settings a lot, then the average is not good enough. You will need to ungroup the images at the and and run one more alignment. The big advantage in my view is that using this exif grouping will result in more cameras aligned because problematic ones can still be solved. The setting that you described simply means that RC groups all the images automatically on import. If you ungroup all of them before alignment, then the results will be exactly the same as if you had switched the setting off.

  • Avatar
    Tom Foster

    Nice explanation, clarifies - I think - but could you just re-write the first sentence, which may have a typo, confuses me a bit anyway.

  • Avatar
    Götz Echtenacher

    I meant that exif grouping makes no special use of lens data, as I thought Mike had understood it...

  • Avatar
    Tom Foster

    So it doesn't refer to the EXIF data imported from camera with each photo, but still works out focal length, distortion (also anything else, I wonder?) from scratch for each pic, then takes the average and applies that to all of the photos that are incuded in an EXIF grouping?

    Whereas, for photos not incuded in an EXIF grouping, it works out and applies focal length, distortion to each photo individually?

    So nowhere is it possible to rigidly state 'this is the EXIF data - trust me - use it just so'?

    If so, sounds like yet another weird, misleading name for a setting.

  • Avatar
    Götz Echtenacher

    I guess that's a matter of how you look at it - it never confused me and I had much less to go on back in the days...  ;-)

    Exif data is never ever enough in photogrammetry - it's only a very rough guideline to give it a name. A bit like saying "look there's a butterfly" instead of  "look there's a Papilio machaon". The real focal length can differ quite a bit, just look at the camera info in an anlignment. So there isn't such a button, only you can give RC more precise data (from a good alignment) and then tell it to apply this rigidly to certain images. But that only works if you change nothing at all from shot to shot.

    Yes, maybe it should rather be named "focal length grouping" but the fact is that it says "grouping" and not something else. It is simply a quick and easy way of getting groups of cameras that are likely to have more or less the same distortion parameters. So yes, if not grouped, RC applies.

  • Avatar
    Steven Smith

    This explains it pretty good and why you want to use it at first then turn it off.

    https://80.lv/articles/full-photogrammetry-guide-for-3d-artists/

    Grouping can speed up alignment, but as Gotz said, it takes and average of the lens distortion from all the photos. Its faster because RC is not trying to calculate each one. But things like lens or sensor stabilization, or even changing focus, will change the mm of even prime lenses. (google focus breathing) Once a component has been calculated, most of the work has been done, ungrouping and under advanced turning on force rematch, RC will then calculate each shot and adjust the position of the cameras to a more accurate model. It is potentially a faster work flow to use it this way. 

    https://support.capturingreality.com/hc/en-us/articles/115001483671-Calibration-groups

  • Avatar
    Tom Foster
     

    "maybe it should rather be named "focal length grouping" but the fact is that it says "grouping" and not something else"

    Indeed, and I v usefuly understand that now, but previously I misleadingly understood something else, so it's not just being pedantic. Needless suffering!

    "you can give RC more precise data (from a good alignment) and then tell it to apply this rigidly to certain images"

    So that is possible, to rigidly specify, and RC obeys?

    Steven Smith said:

    "RC is not trying to calculate each one"

    but doesn't it still have to do that in order to

    "takes and average of the lens distortion from all the photos"?

    All great info, understanding improving - thanks.

  • Avatar
    Steven Smith

    Tom,

    "but doesn't it still have to do that in order to "takes and average of the lens distortion from all the photos"?" 

    This would seem logical, but RC runs on magic not logic. lol. I'm sure there are all kinds of optimizations and complex maths that would require a PHD and a novel to understand. I wish there was a better more in depth guide explaining each setting better than the generic help in the program. As the staff only offers the minimal amount of help in posts ,I believe it is a mix between language barrier (I could be wrong, they are smarter than me)  and not wanting to give away there secret sauce.

    If anyone knows of more articles, web pages, youtube videos, or PDFs that go into more of the settings (more than just take overlapping pictures add control points as necessary and calculate depthmaps) that gives you a deeper understanding of the mechanics at work, I would love to read/watch it.

    I want one of those big manuals like software used to come with. Remember the ones for Windows 3.1 or 95, or like your car. 

  • Avatar
    Mike Simone

    This was the document that guided me to turn it on and cause all my problems:

    https://80.lv/articles/full-photogrammetry-guide-for-3d-artists/

    "Camera grouping by EXIF

    There is no reason not to use this setting. Enabled grouping can help you avoid the wrong camera and lens estimation. RealityCapture calculates these parameters from all images in one lens group. I strongly recommend this for “one camera with prime lens” turntable scans. Grouping is not necessary for multi-camera rigs."

    Other than that issue, that guide is pretty amazing and I would recommend it to anyone getting into or even a vet in photogrammetry.

    I am just not sure why it would cause so many problems as it should only really be a good thing for accuracy. I guess the black magic in RC is just far superior ;)

  • Avatar
    Steven Smith

    That is one of the best articles I have read in a while. That is where I got the idea of using it at first and then ungrouping. Later down the page it reads 

    "Now we have almost all of the images aligned in one component. We can finally refine cameras alignment. To do this, we can ungroup all images and run final alignment. During this step, RC will count all the cameras as different lenses, and adjust the small deviations from the different zooms or sensor/lens shifts from optical stabilization (if you used it).

    During this step, we can decrease the minimal re-projection error. By default, it is 2px. While it is good enough for most datasets, my personal preference is to refine cameras to the at least 1px error. Setting it lower will give a more precise alignment in the mean and median errors. Fewer errors – better mesh, better mesh – less work in post-processing."

    This was the last step I described in aligning that trouble some bathroom with the repeating pattern on the walls form your other post,

  • Avatar
    Mike Simone

    Yeah, I think I didnt realize the importance of this step...

    "We can finally refine cameras alignment. To do this, we can ungroup all images and run final alignment." As their previous comment seemed like it makes sense to just keep it always on.

    I dont normally need to group anything to refine to 1px error anyways so I probably wont use this feature. But I will keep it in the back of my head.

  • Avatar
    Steven Smith

    Agreed, it probably not necessary for project on a fast computer not memory bound, but I have found it helpful on 1000+ photo projects for the time saving, much like using multiple components.

     

  • Avatar
    Götz Echtenacher

    Hehe, runs on magic, I like that!

    Tom, I didn't want to criticize you, just putting it straight.

    On easy objects with a perfect image set, you probably won't need exif grouping. Howecer, mine are usually comlicated with many really difficult corners, so a perfect image set is by definition not possible. That's why I leave it on on principle so I don't lose cameras in those tight spots. With no grouping, there are often problems in those corners, which result in either no alignment or super weird distortion models. Grouping helps all that.

    Steven, I need to give the 1,0 repro error another chance, thanks for mentioning that. I discarded it because in my opinion it doesn't help much with alignment, but it might indeed help with noise.

    And also thanks for mentioning the article, I need to skim that in a quiet minute. Vlad was quite active here on the forum a while ago and really knows his stuff. However, he is a sculpture /small objects guy and that has slightly different requirements and challenges than large scale stuff and especially interiors (the hardest), which we are all interested in.

  • Avatar
    Götz Echtenacher

    By the way, If I dont get 998 out of 1000 aligned on the first go, then I am annoyed - this is how important exif grouping is in my view...

  • Avatar
    Mike Simone

    Just make sure you ungroup and refine your alignment as per the document. 

    Noise is a huge problem when texturing and modeling a large interior room or external structure.

    Thats why I am currently pretty strict about getting a good alignment first and foremost. 

  • Avatar
    Tom Foster

    I keep asking this - is the object of Alignment stage just that - to get the photos aligned - not particularly to get a 'good' point cloud? So that, given good photo alignment, Reconstruction can start afresh, without (much) reference to Alignment's Sparse Point Cloud, to create the final point cloiud, vertices, depth map etc?

    May say, that's academic, why ask - but for instance I might, in a difficult interior, get photos aligned by sticking distinctive objects on the surfaces. Photos would then align using features detected in those objects, but using few features from the actual walls. So the Sparse Point Cloud would contain little info about the actual interior. But with photos aligned, Reconstruction could then have its second go at the photos, and make much more sense of it?

  • Avatar
    Lucia CR

    I would like to comment on your 3rd point: that was one of the first basic video tutorials - https://youtu.be/zfW-8v87Bag

    I cannot recall any other comments like this but there may sure be others, I still reckon this is just an opinion of a few, why pick up on it? we have come a long way since then, focusing more on implementing your feature requests than making videos, trying to help you troubleshoot every day as much as we can with the knowledge and experience we have, maybe more privately due to the sensitive information, following instructions that we have, while juggling loads of other tasks, within a relatively small team of people...

    We do appreciate you being a part of our community and look forward to assisting you as much as we can. This forum is, however, not intented to be a full alternative to our private contact form. Here it is more about discussion with and advice from other users and their experiences. 

  • Avatar
    Steven Smith

    I understand protecting proprietary information. We just want to understand the switches, knobs, and dials we can turn. RC is touted to be one of if not the best photogrammetry software. The one criticism across all the guides and reviews is little documentation and little help. I have noticed the implementation of great new features to your credit (I've been away for a while). I can say most of us just want a better understanding so we can use RC more efficiently and with better confidence. 

  • Avatar
    Steven Smith

    Lucia Benkovicova,

    Can you recommend any guides?  

  • Avatar
    Lucia CR

    we understand that some users would prefer to have a more detailed user guide and specific expert insights readily available everywhere you turn; it does take a lot of time, partnering, and the right people,

    you can find more videos on YouTube (from our users) and elsewhere (we will make a list of some, as well)

  • Avatar
    Steven Smith

    Hey Lucia,

    Come point out all of my mistakes. You know you want to ;)

    https://support.capturingreality.com/hc/en-us/community/posts/360017009192

  • Avatar
    Götz Echtenacher

    Hey Steven, would you mind contacting me via Email? You should be able to find my humble page with my name, or just  "first name (with oe instead of ö)" at "last name" dot "de". Or you tell me how I can reach you, but Steven Smith has a few more hits than my name...  ;-)

  • Avatar
    Steven Smith

    Did I get it right?

  • Avatar
    Mike Simone

    Hey Steven, 

     

    What Camera are you using? I am starting to wonder if my Canon 60D isnt enough to get me what I am looking for in terms of interior photogrammetry...

     

    Or maybe im just making excuses :), sometimes its hard with lower light settings.  But I normally want f/11 and a crisp image, and a full frame camera will give me much better results?

     

    I dont know, maybe im just making excuses haha.. Or could it just be the lens I am using..

  • Avatar
    Mike Simone

    Im just wondering how much a lens would improve things as well.. Maybe I have to goto a professional camera shop and try out a new lens to see.. and get their opinion.

    I feel like the 60D should be good enough, but I always seem to have lots of noise 

  • Avatar
    Steven Smith

    This is also a valuable tool when comparing camera bodies

    https://www.dpreview.com/reviews/image-comparison/fullscreen

    It is important to note glass is important too. Maybe even more so.

  • Avatar
    Götz Echtenacher

    Hey Mike,

    all I can say is that you can get good results with non-professional cameras. I don't see why the 60D should not work for you. It's not on the image comparison Steven linked (one of my favorites) but the 70D has acceptable noise. I got quite good results with a LX-100 and even a FZ28, both Panas. And from what I've seen, you are doing quite good actually. Modern surfaces are very hard if not impossible to capture properly anyway.

    My suspicion is that f11 causes too much defraction (is that the word, Steven?). As I suspected, the D60 has an APSC sensor, which means that your full frame equivalent f-stop is around 16, a number where most lenses have show severe softening. For most cases in our area (buildings), your distance to the object should be so big, that f8 should be sufficient, I prefer f5,6 on my X-T20 since the lens has it's sharpness peak there. Of course, you have to adjust from situation to situation. Another boon is that you get way shorter exposure times. Just try to find some in-depth test of you lens and see which f-stop produces the sharpest results. Maybe that's better than buying a new one? Because not even high end lenses will produce crisp results at f16...

  • Avatar
    Mike Simone

    Well, I ask because if I dont turn on  long exposure clean up, I have a ton of hot pixels. And maybe the lens I currently have should be upgraded to a better prime lens. (If I can find one).

     

    All my photogrammetry is of interior rooms and of buildings. So I need to try to push that f stop to f11 at the least. Im going to play around this weekend to see how good I can take the photos.

    I think it all comes down to rushing it. =/ Some rooms look way better because I took the time, and the first rooms I did I forgot to check a lot before I started. Or the focus becomes off ...I think I need to tape it next time.

  • Avatar
    Götz Echtenacher

    Hmm, hot pixels are a problem. But again, that would not be as bad with a smaller f-stop.

    I'm not sure if it's really neccessary to focus (pun intended) so much on a huge DOF. As long as the fore- or background is not completely blurry (as in only color gradients, which is hard to schieve, even if intended), then RC will stilll be able to find features for alignment. And there is no benefit to have far away surfaces crispy sharp when you have them again much closer, cause RC will use those then.

    I think taking more care with shooting is probably the best way to go. I have difficulties in that respect myself - can never be fast enough. But I also need to change that...

    Better lenses are always better!  :-) So no harm doen there.

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