CODEWITHSUNDEEP
pythonopencvimage-processingsize
mail 44
mail 44

Reputation: 21

Measure object size without reference object always in frame

Is there a way to measure size of the object without having the reference object (Aruco marker/coin) always in the frame? As in after calculating the pixel per metric ratio, can we use this value only to compute the size of the object? The camera will also always be from a fixed height. Thanks so much!

Upvotes: 2

Views: 1792

Answers (1)

YoniChechik
YoniChechik

Reputation: 1537

The short answer is no. This problem occurs in 3D->2D projection (also called homography or perspective projection). Here is an example:

perspective manipulation1

Here is a simplified version of this projection:

enter image description here

As you can see- if you decrease z but increase x&y you can get the same result, even though you know the pixel-distance ration (that is f in the equation).

check out this two links for a more mathematical proof.

For measuring in 2D images you first need the f (intrinsic calibration) and also one of two: By knowing a size of an object in the screen (like the aruco) you can infer z, and if you know z of the object (=distance from the camera) you can infer size.

Upvotes: 1

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