[SOLVED] Angular measurements seem near impossible for me...

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Ulicad
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[SOLVED] Angular measurements seem near impossible for me...

Post by Ulicad »

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See further down for the original post:
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When trying to check / measure an angle between expectedly two parallel lines, the result of the measurement (using WB Part) appeared to be faulty to me and a feeling crept in: How can I trust Freecad in other aspects... - while the cause for the problem definitely originated from my head...

Following a request for help, @Roy_043 had given the first clue for the cause of the presumably "can't be" measurement or, in other words, my inability to measure a "simple" angle: -> ...the two lines selected for the measurement may not be located within one plane only (x/y-plane in this case)...

This exactly was the case. Being absolutely not aware of this fact, the reference line did look perfectly parallel to the x-axis, while viewing it from TOP. But this was not the case in 3D. Viewing from almost any other perspective, it became obvious, that the reference line was NOT parallel to the x-axis. Thus, resulting in a completely unexpected angle.

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Original post:
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Hi everyone here of the patient helpers!

To introduce myself in brief:
- engaged doing all sorts of things by personal interest only
- some technical background is there
- retired - is it that how it's called usually?
- trying to make some sense of the functions in Freecad
- intending to use it for few particular purposes from time to time only (having searched many hours already here and elsewhere though)
and so forth...

Using Freecad 0.20.1 on WIN 10 actually.

Now here only one of the myriad question marks / problems encountered, which may reduce the riddles a bit:
As can be imagined on the image attached, the base angle of the object is 0° - parallel to the x-axis (at least I almost would swear..).
Yet, the angular measurement is showing some 1.88... degrees - way off 0°. I several times tried to select the two reference lines correctly (a mistake here hardly is possible), but it never showed 0° (zero degrees).

Would one of you have an explanation for this behaviour?
It possibly could solve a whole lot of my mislead or straightly wrong thinking.

After many hours of hacking around I gladly would appreciate any help!

So long Uli
angle-measurement1.jpg
angle-measurement1.jpg (195.99 KiB) Viewed 1119 times
Last edited by Ulicad on Sun Aug 21, 2022 8:46 pm, edited 2 times in total.
Regards, Ulicad / Uli
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Bance
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Re: Anglar measurements & rotation seems near impossible for me...

Post by Bance »

All very interesting, how about helping us to help you?

http://forum.freecadweb.org/viewtopic.php?f=3&t=2264
Ulicad
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Re: Angular measurements & rotation seems near impossible for me...

Post by Ulicad »

Hello Bance, thank you for your reply!

I already had read this post you referred to beforehand and and would not know what is missing to make myself understood?

Basically, not to be mistaken:
I truly love the idea of open source since *many* years and truly appreciate the work of millions of people working on such projects.
Only with the first steps in Freecad, I simply am overwhelmed actually...

Would you be so kind and let me know what is missing so I can improve it?

May be, I can put in in other words beforehand:
1) What is understood:
An angle between two parallel lines can't be calculated (similar to a division by zero).

2) Now, Freecad seems to have calculated this "non-angle" to a value of approx. 1.88 degree.

This makes me really nervous about the usability / reliability in the ordinary use, if precision for small values is required (down to 1/100 mm - 0.00039 in approx.). Is there an explanation to clarify this behavior? It may lead to solve other riddles on my side as well.

Hope this is making it more clear?
Regards, Ulicad / Uli
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Bance
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Re: Angular measurements & rotation seems near impossible for me...

Post by Bance »

Ulicad wrote: Fri Aug 19, 2022 6:24 amI already had read this post you referred to beforehand and and would not know what is missing to make myself understood?
And yet none of the required information was provided....

What is your version information as stated in the above link?

Which WB(s) are you using?

Where is a file or MWE(minimum working example)?

Have you been following tutorials, if so which?

Are you using snapping?
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thomas-neemann
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Re: Angular measurements & rotation seems near impossible for me...

Post by thomas-neemann »

Ulicad wrote: Thu Aug 18, 2022 8:54 pm ...

I would do it like this


https://www.youtube.com/watch?v=YEGvOUf_2Ho

phpBB [video]



Code: Select all

OS: Ubuntu 20.04.1 LTS (XFCE/xubuntu)
Word size of FreeCAD: 64-bit
Version: 0.20.29177 (Git) AppImage
Build type: Release
Branch: (HEAD detached at 0.20)
Hash: 68e337670e227889217652ddac593c93b5e8dc94
Python 3.9.13, Qt 5.12.9, Coin 4.0.0, Vtk 9.1.0, OCC 7.5.3
Locale: German/Germany (de_DE)
Gruß Dipl.-Ing. (FH) Thomas Neemann

https://www.youtube.com/@thomasneemann5 ... ry=freecad
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Roy_043
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Re: Angular measurements & rotation seems near impossible for me...

Post by Roy_043 »

Looking at the statusbar in the image in the OP we see a non-zero Z coordinate. So perhaps the lines are not on the same plane?
Ulicad
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Re: Angular measurements & rotation seems near impossible for me...

Post by Ulicad »

Thanks Roy! This is a promising clue, probably leading to understand the matter better.

If any of the regarding lines are not placed *exactly* and fully within the x-y-plane, this "deviation" would become obvious.

BTW:
Until now, I could not find where in the screenshot you detected a y-axis different from 0°???

I want to go through all said above and be back asap.

Thanks again!
Regards, Ulicad / Uli
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Re: Angular measurements & rotation seems near impossible for me...

Post by Bance »

If the lines are parallel, plane has nothing to do with it.

Everybody is just guessing, because there has not been enough information supplied in the first place!
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wandererfan
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Re: Angular measurements & rotation seems near impossible for me...

Post by wandererfan »

Ulicad wrote: Thu Aug 18, 2022 8:54 pm Would one of you have an explanation for this behaviour?
The angle measurement tool measures the angle in 3D. Rotate your view to see if the lines you are measuring are in the same plane.

You'll get better answers faster if you include a FCStd file showing the problem.
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Re: Angular measurements & rotation seems near impossible for me...

Post by Bance »

Parallel lines different planes......
parallel.png
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