Projection of vector on a plane

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Discussion Overview

The discussion revolves around finding the perpendicular projection of a vector onto a plane in three-dimensional space. Participants explore different methods and approaches to achieve this projection, including mathematical formulations and geometric interpretations.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • Some participants propose that the projection of a vector onto a plane can be found by projecting both the origin and the endpoint of the vector onto the plane using the normal vector of the plane.
  • Another participant suggests that to find the projection, one can calculate the dot product of the vector with the plane's normal and then adjust the vector accordingly to find a point on the plane.
  • One approach mentioned involves finding the projection of the vector onto the normal vector of the plane and subtracting this from the original vector to obtain a vector that lies parallel to the plane.
  • A later reply introduces a related question about finding the minimum distance from a point to a plane, indicating a potential connection to the projection problem.

Areas of Agreement / Disagreement

Participants express various methods for calculating the projection, but there is no consensus on a single best approach. Multiple competing views on how to set up the problem and the steps involved remain evident throughout the discussion.

Contextual Notes

Some participants' methods depend on specific forms of the plane equation and the definitions of vector operations, which may introduce limitations or assumptions not fully explored in the discussion.

Curl
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How do I find a vector which is the projection of another vector onto a plane?

By projection, I mean perpendicular projection onto this plane. I know that this vector must lie in the plane and have a minimum angle with the original vector, but it seems like setting up the problem in this manner is unnecessarily messy. There should be another (better/faster) way.
 
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Curl said:
How do I find a vector which is the projection of another vector onto a plane?

By projection, I mean perpendicular projection onto this plane. I know that this vector must lie in the plane and have a minimum angle with the original vector, but it seems like setting up the problem in this manner is unnecessarily messy. There should be another (better/faster) way.

I think you would have to project two points on to the plane: the origin and the end point of the vector. You can do this by calculating the dot product of the points with the normal of the plane and subtract that component in the direction of the normal.

In other words d = n . p and the point on the plane = p - d x n which should lie on the plane.

For the origin, if you have the plane equation in the form of ax + by + cz + d = 0, then you have to calculate the point -n.d. These two points should allow you to construct a vector that lies on the plane.
 
Given a plane, say, A+ By+ Cz= D, the vector v= Ai+ Bj+ Ck is perpendicular to it. Find the projection of the given vector, u, on that vector and subtract from u. Since you have subtracted off the "orthogonal projection" to the plane, what is left will be parallel to the plane.
 
Given a point (x,y,z) in R^3, how do I find the minimum distance between it and a plane?

It seems I forgot all these things.
 

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