Connecting rooms through doorways + Inspection tool

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    Tom Foster

    Bingo! some real intelligible discussion on the subject (starting with Gotz' "Just try it out"). Will take some careful reading.

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    tingelbobber

    I think its a bit missleading because red means most of the time error or failue, perhaps rename the button to „inspect connection heatmap“ and its all fine, red high temperature, blue cold low temperature.
    Great thread!

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    Tom Foster

    "red means most of the time error or failue"

    I'd love to know how you know that?

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    tingelbobber

    I mean, in general :) just ignore my comment.

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    Tom Foster

    Zuzana said:

    "The most important thing to check with Inspect tool is the number of created virtual components with the component connectivity set to at least 4. This means that if the images are connected into one virtual component with the component connectivity set to at least 4 (that is the reason why the default value is 4), the alignment can be considered as stable and no cracks or misalignments should appear."

    This is very good, useable advice. So even if in Alignment all or nearly all photos have registered into a single Component, if in Inspect it's still split into several 'Virtual Components', it's still not a robust Alignment? and needs more photos.

    (It's really unfortunate, two completely different uses of the word Component - and so close together in the process. Confusion guaranteed?)

    Now, I can fiddle this. I can get all cameras into one single Virtual Component, "with the component connectivity set to at least 4", without adding photos but simply by reducing Matches count: "Matches count – two cameras are connected into one component only if there are at least this number of common features (matches) among those two cameras." I reduce default Matches count from 100 to 49 and suddenly it turns out that sufficient camera pairs have at least 50 matches, and so all can unify into a single Virtual Component (and a couple of detached solos).

    Of course, this fiddle doesn't change Alignment at all, is just a way of Inspecting it.

    But just as it's important that single Virtual component is achieved @ default Component connectivity 4, how important is it @ default Matches count 100?

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    Tom Foster

    Zuzana said:

    "If there are several virtual components ... we would recommend to add images in these areas."

    With multiple Virtual components, the different camera colours aren't distinct enough to get a mental image. I assume that's how I should decide where are "these areas" that I should add photos? What am I looking for? I'm seeing no gaps between virtual Components - they are intermingled.

    Also it's very hard to count the multiple Virtual components, by hovering the mouse to see what highlights - or is that not useful anyway?

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    Tom Foster

    Thanks a bundle, both Zuzana and Gotz - makes a huge difference.

    But still missing for me is Feature consistenncy and Apical angle - "Those features however have to suffice the condition defined by apical angle and Feature consistency."

    Also Internal vs External edges vs Both?

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    Zuzana Ďuríčková CR

    Hello everyone,

    @Götz Echtenacher

    „Concerning Maximal Count: I think it's important to mention that the value will not result in fewer lines, just move the color threshold for red down to this number. That means all image pairs with more than e.g. 1000 matches will also be red.“

    Changing Maximal Count value can result in fewer lines and also the color scale is recomputed. You can see the illustration in the picture below.

     

     „So Connectivity means how many "partners" each camera has?“

    If one camera has less connections with the cameras in the virtual component, it is not included in this component. If the camera has let’s say max. 2 connections with the cameras inside one virtual component and the component connectivity is set to 3, then this camera is not attached to the component.

    “Also, is it correct to assume that if Maximal Count is left blank, red will be the connection with the most tie points in this model?”

    Yes, it is correct.

    @Tom Foster

    „But just as it's important that single Virtual component is achieved @ default Component connectivity 4, how important is it @ default Matches count 100?“

    Edge within one component has to have at least this number of matches. RC takes a feature, if this feature is visible in defined number of images (Feature consistency) and if the angle among the pairs of cameras is bigger than the angle defined by Apical angle, the matches count for the edge is raised by one. Matches are the features that suffice these two conditions.

    You can also analyze only selection of images if the Analyze selection is set to ‘True’. You do not need to actually count the components, you need to see if there are gaps among them or if there are separate virtual components in any part of the model.

    “Also Internal vs External edges vs Both?”

    Internal edges are the edges inside the components, External edges are the edges outside components, the ones connecting individual components. If you use both, then you can see all the created edges (the grey ones are internal, the colored ones are external).

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    Götz Echtenacher

    Dear Zuzana,

    again, thanks a lot for the answer! I apprecitate the recent activity of you guys at RC very much.

    Hmm, ok, so no lines above the Maximal Count threshold. Good to know. Would it not makes sense to add another variable where one can simply define the point from which on all the lines will be red? Because that would have the advantage that the color range can be made more useful (usually most lines are blue) without losing some vital information.

    >>„So Connectivity means how many "partners" each camera has?“

    If one camera has less connections with the cameras in the virtual component, it is not included in this component. If the camera has let’s say max. 2 connections with the cameras inside one virtual component and the component connectivity is set to 3, then this camera is not attached to the component.<<

    So the short answer to this question is also yes? Or did I miss something?  :-)

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    Tom Foster

    Does Apical angle relate to Cameras, or to Feature matches?

    Is Apical angle

    a) the included angle between the axes of any two Cameras?

    Or is it, for the same Feature seen in (forming a Feature match between) any two Cameras,

    b) the included angle between their two projected lines? (Projected line runs from Camera eye-point, through the Feature; the two projected lines converge, pass close; Tie point is the place where they come closest).

    a) and b) will differ. I'd think that b) is more relevant to RC than a)?

    If Apical angle is b), the smaller the angle then the more error-prone is the location of the Tie point in the depth map. Is that why the Apical angle setting an 'at least' filter? i.e. if set to 3o, Feature matches whose projected lines converge at 2o will not qualify?

    Default 1o sounds horribly error-prone to me - basic trigonometry.

    Apical means 'at the apex'. Yet it's infinitely rare for either a) or b) to actually meet, to form an apex. They just pass close.

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    Zuzana Ďuríčková CR

    Hello,

    @Götz Echtenacher

    "So the short answer to this question is also yes? Or did I miss something?  :-)"

    Yes, sorry I got carried away with the explanation :)

    "Would it not makes sense to add another variable where one can simply define the point from which on all the lines will be red?"

    I agree, it could be useful information. I will forward it for discussion. Thanks.

    @Tom Foster

    "b) the included angle between their two projected lines? (Projected line runs from Camera eye-point, through the Feature; the two projected lines converge, pass close; Tie point is the place where they come closest)."

    This is correct, it is an angle created by two projection lines (from two cameras) and the tie point is vertex of the angle. 

    "If Apical angle is b), the smaller the angle then the more error-prone is the location of the Tie point in the depth map. Is that why the Apical angle setting an 'at least' filter? i.e. if set to 3o, Feature matches whose projected lines converge at 2o will not qualify?"

    This is also correct. 

     

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