1 Topic by pauloliveira

  • pauloliveira
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Hi Joan,

How are you?
I need to know, when you convert pixel to metric unit, if you calibrate a horizontal line, the system is calibrate in vertical?
I make some tests, but I do not believe in some values, but I would liked listen your opinion.

Thank you for your attention.

Best wishes

Paulo Oliveira

2 Reply by joan

  • joan
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Hello,
The calibration by line does not have any notion of horizontal or vertical. It maps a 2D distance in pixels to a distance in the specified unit. At the bottom of it it is just a scaling factor from pixels to centimeters or whatever. 2D distances are computed using the usual Euclidean distance.

This can give wrong results if you have a video with rectangular pixels that has not been automatically detected, (video looks squashed or stretched). More commonly, if the plane of motion is not perpendicular to the camera optical axis. For this you can use the perspective coordinate system.

3 Reply by pauloliveira

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Do you have a explanation about "How calibration with perspective coordinate system"

Thank you for your answer.

Best regards.
Paulo Oliveira

Paulo Oliveira

4 Reply by joan

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1. Add a perspective grid
2. Place its corners on the corners of a rectangular object visible in the scene and on the same plane as the plane that you want to make measurements on.
3. Right click the grid and use "Calibrate", enter the physical dimensions of the rectangle.

You can display the coordinate system with Image > Coordinate system.