Proper workflow to solve misaligned cameras?

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    Götz Echtenacher
    Hi Steven,

    did you group your images by exif?
    That can sort out initial misalignments like that.
    It might be necessary that you delete all components first though (but in a new project of course).
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    steven verver
    Hi, no i set "camera priors" to "disable" if you mean that.
    I tried it as well with "enable" but to no resolve.
    Any other suggestions on how to solve this?
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    Götz Echtenacher
    I've never worked with the camera priors setting before.
    What I meant is to group the images by exif on import, that means for each camera / focal length there is a different group which will use the same distortion values. As a result, there should be no erroneous distortion/localisation if the tie points are not ideal on some images, like it seems to be the case with your troublemakers.
    You can also do that manually after import - just go to 1D view and select all images with the same focal length and camera, then set the values Calibration Group and Lens Group to something other than -1 (which is standard and means calculate the distortion for each image individually), usually the values are both the same.
    It may be neccessary to delete all components before it works because RC might hold onto the false ones if the component is still present. Then you can ungroup them again when you are certain that all are in the right place and run another alignment, which will usually increase the accuracy...
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    steven verver
    Hi, I've used a zoom lens to take these images, with different zoom levels.
    So the images are taken with the same lens, but with a different focal length.
    I can see this different focal length in the "focal length" field under "prior calibration", some are 85mm, others 135mm (see the attchment).

    overview2.png


    So would assigning them to one calibration group make matters worse?
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    Götz Echtenacher
    Yes, if you stuff all of them in the same group it is very bad! :-)

    But the idea is to use one group for each focal length.
    Best practice for Photogrammetry is to use a fixed lens.
    I don't do that myself, I use zoom as well.
    But then you should restrict your zoom steps to a minimum, ideally beginning and end.
    I don't do that myself, but one of my cameras supports zoom steps and with the other I make sure that I take as many images as possible with an intermediate focal length. You definitaly need at least a handful with the same setting, the more, the better. And the fewer you have, the more important it is to put them all into a group.
    So click on Images and select all the ones with the same length (ctrl lmb) and set the first one to 1, the second to 2 etc.
    Then realign.
    Or just create a new project and set Group by Exif (or similar) to True before you drag the images in.
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    steven verver
    Ok lots of thanks for your help, this did the trick!
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    Götz Echtenacher

    Glad it worked!

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