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Author Topic: How to use ruler for precise measurements?  (Read 581 times)

maurello

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How to use ruler for precise measurements?
« on: August 02, 2022, 06:08:01 PM »
I used scale bars in the last model created in order to then take precise measurements afterwards.

How do you take a measurement in Metashape in a plane or parallel to a plane (= like the plane of the display)? I have not been able to discover that. I try to make engineering drawings of the model. With great care, I placed the model parallel with X-Y plane as much as it was possible. For the model dimensions, dimensions A, B and C need to be in or parallel to X-Y plane. That is that A and (B & C) are ortogonal defining max dimensions in X- and Y- directions.
But the Metashape "ruler"-tool doesn't allow free measurements. It doesn't give you the option to freely measure distances between free points (whatever coordinates) in 3D space (like points in X-Y plane). The "ruler"-tool sticks only to model points, which means that it is practically impossible to measure distances of points projected into a preferred plane, but the measured distance has always some angle to wanted plane. Hence the measured distance has also a component in Z-direction. So there will be always an error caused by that angle (= ~cosine of the angle between measured distance and X-Y plane).


maurello

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Re: How to use ruler for precise measurements?
« Reply #1 on: August 26, 2022, 09:17:12 AM »
Any help on this one?

Alexey Pasumansky

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Re: How to use ruler for precise measurements?
« Reply #2 on: August 26, 2022, 12:46:48 PM »
Hello maurello,

If you need to take measurements in a specific plane you can create three markers that lay in that plane - just input their coordinates to the Source values tab of the Reference pane, check them on, but do not define any projections on the images. Then select those markers in the Model view, right-click and select Set Drawing Plane option from the context menu. You will see the plane (defined by the certain color) and new shapes being drawn as well as the ruler measurements will be performed based on the point placed on that plane.

Let me know, if you are able to set up the drawing plane and the results of the measurements on it fit your needs.
Best regards,
Alexey Pasumansky,
Agisoft LLC

maurello

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Re: How to use ruler for precise measurements?
« Reply #3 on: September 13, 2022, 08:08:16 PM »
Hello maurello,

If you need to take measurements in a specific plane you can create three markers that lay in that plane - just input their coordinates to the Source values tab of the Reference pane, check them on, but do not define any projections on the images. Then select those markers in the Model view, right-click and select Set Drawing Plane option from the context menu. You will see the plane (defined by the certain color) and new shapes being drawn as well as the ruler measurements will be performed based on the point placed on that plane.

Let me know, if you are able to set up the drawing plane and the results of the measurements on it fit your needs.

This sounds quite tricky. How can I secure the plane create is parallel to the model?
We recreate underwater models of shipwrecks, so the input material has a lot of noise in it. Furthermore we do not have "ground" or any reference point to create plane. It would be an arbitrary choice of coordinates in space. Unless I did not understand what you suggest.