Q. What is a reference?
A. A reference can be any object in the scene whose length can be easily and accurately measured (a door, a window, a table, etc.).
Q. Do I really need to measure something? Why cannot I just give you two pictures?
A. Theoretically speaking, you cannot obtain true 3D dimensions without knowing at least one true length.
Think this way: If one views a video clip of, say, the Grand Canyon, it is not possible to ascertain if the video was shot from a helicopter flying over the true landscape in Arizona or if the video was synthesized in a Hollywood movie studio using computer graphics techniques based on a scale-down model of the Grand Canyon - if the model is sufficiently detailed and photo-realistic. Hence, it is not possible to obtain true 3D dimensions without a reference length of some kind.
Q. How many references do I need?
A. Currently, the metrology engine will take only one reference.
Q. Do I need to use an object already in the scene as the reference or can I place something (e.g., an umbrella) in the scene and use it as the reference?
A. Both are ok.
Q. Do I need to see the reference in the two pictures? Can the reference be partially occluded by other objects?
A. Yes. As long as the end points of the reference are clearly visible in both pictures, it can be partially occluded by other objects in the scene.
Q. Can the reference move in the two pictures?
A. No. The reference must be a stationary object in the scene.
Q. Should the reference be placed at a certain location in the scene?
A. The reference object can be anywhere in the scene. However, a reference that is physically close to the objects that you want to measure can usually provide better metrology accuracy.
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