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jsiggia

Query an ellipse angle.

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Hi Z,

Is it possible to query the degree of a drawn ellipse? I think this might be useful when modeling from photos. An ellipse in a photo can be traced to determine the angle the original circle was photographed at.

 

Thoughts anyone?

 

Thanks for reading,

Joe

 

 

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Trigonometry to the rescue.  

 

Measure the minor axis and the major axis and divide them to get a ratio  - - -   minor/major      then plug that ratio into the arcsin(ratio)  function.

It is the ratio that counts, not the actual size or units.   So, it could be measured on-screen.

So, if you measure a circle that is laid back to appear as an elips and the minor axis is 1/2 of the major axis     arcsin(.5)  =  30º      If it were facing you directly on so that you see the whole circle   5'/5' = 1     arcsin(1) = 90º

arccos give you the other perspective   arccos(1) = 0º   arccos(.5) = 60º  (so, which you want to use depends on from which angle you want to measure)

 

arcsin:  https://www.rapidtables.com/calc/math/Arcsin_Calculator.html

arccos: https://www.rapidtables.com/calc/math/Arccos_Calculator.html

 

It would work for other shapes too, as long as you know what the shape is and how to figure out that ratio.  (square would be the exact same as the circle)

If you want to know more on why this works, I could give a more in-depth version.

 

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Thanks Chris,

Thanks for your explanation & the calculator links.

Was hoping ADS. might add this to the object information or Measure Quantity tool?

 

Joe

 

 

 

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Ah!  Agreed, something like that would be of aid.    Not sure how far the python API will take things, but if it makes sense, I could add an additional tool.  Pretty sure it won't let me modify existing tools.

 

¢£

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Nice Des,

Now imagine one of these in a biker bar & two dudes start getting into it because one of them hit the ball too hard and distorted the ellipse 😎

 

Joe

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One possible caveat is that such a circle might be 3d- tilted, compared with the rest of the scene, or itself warped illusively because it is on a 3d warped surface, no? Such that a more complex tool would need pictures taken from several differing viewpoint angles, or multiple shots taken from known viewpoints with precicely angular relationships, all calculated by sensors and software.

.cadmeraScreens.gif

The blue dots represent cameras viewing a rectangular scene, and may calculate precise dimensions within the volume; and, the cameras would communicate together to determine cones of vision, to use in modeling content in a modeled rectangular or other modeled space, (like a room). The image is actually from a formZ Multi-View screenshot, taken many years ago, (when Multi-View might have had a different name and we used the acronym CAD;)

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