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I have been working on old aerial photos on Agisoft Metashape and there is a button that company added this called the "show" point residuals. When you turn it on, it shows where the line shows. I downloaded their software manual version from their website and have search for more information about it, but it is not on their manual

I am trying to understand this and how it works…

For example, if you have the control points on several ungeoreferenced imagery and then you plot spread out the control points. You put down around 20 of them and you turn it on. If you found one that has 3 different lines on three imagery and should I need to fix it?

You can see what I am drawing here is that if you see imagery 1, I move my control points from A to B. Same thing with imagery 2 and 3

Is that what am I suppose to do? or do I need to leave them alone.

Here is the attachment

enter image description here

if you have some links that might be very helpful.

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I don't know this specific software, but in photogrammetry each image will be adjusted according to the model that minimizes the square of the errors. The residual that is shown indicates how much error you make with this model (difference between the position of the control point and the position of the control point as predicted by the model). I don't see the scale so I cannot tell if this is large or acceptable, but a rule of thumb is to have an root mean square error that is smaller than the pixel size. This does not prevent from locally large errors but means that your image is overall OK. Now, because the images have different viewing angles, they each have a different model, which explain why the lines are not pointing in the same direction. This is of course ennoying, but sometimes it isnot possible to achieve better accuracy.

In any case, moving all GCP where the model predict that they will be, give you a nice RMSE (0) but in fact this will not improve the model (on the opposite, the model will be less good). that being said, it can be useful to control the quality of the control points (if one is very far from its predicted position, maybe the error comes from the point and not from the model), therefore some points can be moved if you have a good reason. Otherwise, changing the type of model or adding new control points could help.

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  • Thank you. What about the image size for each one ? I have 10 of them have different sizes . I am talking about the dimensions such as width and height ?
    – PROBERT
    Mar 11, 2020 at 20:28
  • sorry, I don't understand your comment. Which images are you talking about ?
    – radouxju
    Mar 11, 2020 at 21:52
  • My questions is I have 10 of my images on my software showed me have different dimensions for each image width and height ? I tried to copy and paste the screenshot here....not sure how
    – PROBERT
    Mar 11, 2020 at 23:49

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