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Measure and Scale?

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  • Measure and Scale?

    I am wondering about 3DF Zephyrs correct way to scale an object.

    My way of thinking is as follows: I would ignored correct scaling until I have reconstructed a Mesh. On the Mesh, I'd simply want to measure to points (from which I know the real world distance) with the "Quick Measurements" tool. Then I'd like to tell Zephyr: "Hey, the distance of this 2 points is not your measured value X, but instead I am telling you now that is value Y." and I would want Zephyr to scale the entire model in all dimensions accordingly. Is something like that possible?

  • #2
    Hi Josua,

    what you described is rescaling via control distances. There are two ways:

    - the first one is to place control points in your scene (which can be with markers you measured, or any other known distance in the scene, e.g. the height of a door) and pick those points in 2D from the images to create the control points in zephyr. Then, add them as control distances, and use the scale world using control distances function. This is the preferred way and the most accurate way using control distances, available in zephyr Pro and Aerial only. Tutorial on control points and distances is available here :

    Note that scaling using control distances is a rigid scaling, so you will not change any camera position at all. If you have the 3D coordinate of your control points (e.g. by using a total station) then you can also use that information to drive the reconstruction in the SfM stage, which will act and potentially change/aid the camera calibration

    - the action you described, to pick the distance in 3D, is by nature not accurate and won't allow you to measure the accuracy of the rescaling operation (as you will do it only on two points, and thus, you won't be able to compare it to other control distances and calculate the residuals) and is generally used where accuracy is not a big problem (e.g. for 3D printing) and can be done exactly as you said by following this guide


    • #3
      Thank you for the competent answer!