Common pivot point and/or intersecting planes

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Common pivot point and/or intersecting planes

Postby Exouxas » Mon Jan 09, 2017 1:49 pm UTC


If I have an object with position p1 (center of object) and angle a1, then move it on a pivot point and get position p2 (center of object) and angle a2 would I be able to get the"local" offset from p2 to the pivot point?

As an example object, take a nokia 6110. The tip of the antenna could be the pivot point and the center of the phone is where the position is.

The offset would be around x:2cm, y:7cm, z:0.5cm

But how could I calculate this by moving from one position to another and keeping the tip of the antenna in the exact same position?

If you don't want to explain how to do it specifically, you can send me links to what this is called, or just post the name.

My thoughts so far:
I thought that I might need to treat each of the objects position and angle as a plane, creating two planes that will intersect and have one single common point which would be the position of where the pivot point is. But I don't know much about this and I might be completely wrong. Also I have no idea how I would calculate that.


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Re: Common pivot point and/or intersecting planes

Postby eran_rathan » Tue Jan 10, 2017 1:25 am UTC

Its called coordinate geometry (or, to surveyors and engineers, COGO).

If the tip of your antenna was at (0,0,0) and the center point would be (-2,-7,-0.5) (assuming you are holding the phone upright and the faces of the phone describe your orthagonal planes).

Rotation on one of the faces would be based on the sine of the angle of rotation applied to the distance from pivot to p1 (which is r, which is √(Δx2+Δy2+Δz2),) in this case you are describing a sphere of all possible rotations:


where (x2,y2,z2) is the new position. Translating the angles to the coordinates is via the sin, cos, tan functions, which I'm too tired to really go into at this moment.
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Re: Common pivot point and/or intersecting planes

Postby Exouxas » Tue Jan 10, 2017 8:29 am UTC


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