How to precisely align orthophoto camera?

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    Lucia CR
    Jan Ström wrote:
    I am new to RC and photogrammetry in general. My main interest is rendering correct orthophotos of architectural facades.
    I have been reasonably successful in my first try-outs - but I have so far ony been able to manually align the model so that the facade is parallel with the bounding box, i.e. the orthophoto "camera". And by "manually" I mean just eyeballing the bounding box and the model and correcting until it "looks right", like they are in parallel.
    That seems not to be enough. When I inspect my renders I find slight imperfections to the rectified photo. The problem is that all lines which should be parallel, in fact isn't really. I suspect the manual alignement of bounding box/model to be the reason. If there is misalignement the lines in the orthophoto would be not quite parallel.

    I might have missed a function somewhere which could align the house model more precisely with the bounding box - Can someone enlighten me? Thanks in advance.

    Hello, I would start with this information - how to take pictures: Taking pictures for photogrammetry (actually being extended - waiting for approval). If taken properly, there is usually no need to correct anything manually.
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    Wishgranter
    Hi Jan Ström
    In short, you have set up a bounding box (BBox) and calculated an ORTHO projection and since then you can see some distortion in the models-ortho, so it is not a properly calculated ortho image ??

    Is it possible to see any screenshots of the actual issue ?
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    Jan Ström
    The problem is this: I made a test from 20-odd photos of a facade and a roof of a small 18th centruy farmhouse. I expected the orthophoto to have 90 degrees corners and entirely parallel lines for - for example - the left and right side of the roof, and all other lines on a orthophoto of a house that is supposed to be parallel. Like an architectural drawing.

    Facade-1.jpg


    When I placed that photo in a graphic program and superimposed a grid, it is evident that the left side of the roof is not straight. it "leans inward", like you would expect if the photo was a perspective one, not an orthophoto. It is just a little bit, but it should not be there.
    The right hand side of the roof is OK. So something must be wrong in the set-up of the ortho camera. The "film plane" of the ortho camera is not parallel to the house.

    I did not make screenshots when I made this actual rendering, but I worked hard to fit the Bbox to the house, so that it looked parallel, but I could only eyeball it, and it was not easy.

    I made a somewhat exagerated second try just to show what I mean:

    wrong_bounding_box.jpg


    This Bbox is clearly misplaced. It is wrong in two dimensions. When I make an orthophoto with this Bbox, it turns out like this:

    facade_Wrong bounding box.jpg


    Aside from that it is not cleaned up, it shows the effect of both wrong placed axis. Tho roof is far too low, because the Bbox "leans outwards". And - exagerated as it is - you can clearly see that the left and right hand side beams of the roof are not parallel.

    Question is still - is there a way to place the Bbox exactly parallel to - in this case - a house facade?

    /Jan
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    Wishgranter
    Hi Jan Ström
    We have implemented TRUE ORTHO algorithms so we calculate PROPER ORTHOS. If you are experienced and, as it is not a big science, the BBOx is placed and oriented quite well even with just UI ( use RECONSTRUCTION-INFO PANEL to change it by precise values )
    The projection can be wrong because of real "distortion" of the building or, as you are mentioning, just the 20 image dataset...

    Or if you are interested, send me the data + RCPROJ to milos.lukac@capturingreality.com for inspection...
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