Parametric Description of a Plane

In summary, a plane is a point and two vectors with the equation being plane sum = {OP + tv + sw} where v and w are vectors and t and s are real numbers. This is called the parametric description of the plane.
  • #1
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I read the definition that a plane is a point and two vectors with the equation being plane sum = {OP + tv + sw} where v and w are vectors and t and s are real numbers. This is called the parametric description of the plane. I haven't seen the equation in this form before though.

Can someone explain what these values stand for/how to use this equation or direct me to a page that explains it? I just see the regular plane equation when I google this.
 
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  • #2
You are aware that a plane can be defined by three points that are not co-linear?
This form is just the same - using two pairs of points to form the two vectors.

Any two vectors ##\vec v## and ##\vec w## must lie in a common plane.
In fact, they can define a set of parallel planes.

The parametric equation is just the instructions to get to another point in the plane starting from where you are at.

i.e. If point ##P## is in the plane defined by the above vectors, then you can get from there to point ##Q##, also in the pane, by starting out at ##P## and walking ##t## steps of size ##v## in the direction of ##\vec v##, then turning to the direction of ##\vec w## and walking ##s## steps of size ##w## in that direction.

In maths that is: ##Q=P+t\vec v + s\vec w##

Concrete example:$$\begin{pmatrix}x\\y\\z\end{pmatrix}=\begin{pmatrix}1\\-1\\2\end{pmatrix}+t\begin{pmatrix}3\\4\\0\end{pmatrix}+s\begin{pmatrix}-1\\0\\0\end{pmatrix}$$... tells you how to get to point (x,y,z) from point (1,-1,1) using (3,4,0) and (-1,0,0) as cardinal directions.

i.e. you want to get to (x,y)=(8,8), then t=2 and s=-1
so you must travel 10 units along the hypotenuse of the 3-4-5 triangle, then 1 unit parallel to the x-axis.

Notice that the plane in the example is parallel to the cartesian x-y plane, and have expressed the vectors in cartesian coordinates. I don't have to.

The directions done this way basically translate the (t,s) coordinates for positions on the plane to (x,y,z) cartesian coordinates ...
 
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  • #3
Simon Bridge said:
You are aware that a plane can be defined by three points that are not co-linear?
This form is just the same - using two pairs of points to form the two vectors.

Any two vectors ##\vec v## and ##\vec w## must lie in a common plane.
In fact, they can define a set of parallel planes.

The parametric equation is just the instructions to get to another point in the plane starting from where you are at.

i.e. If point ##P## is in the plane defined by the above vectors, then you can get from there to point ##Q##, also in the pane, by starting out at ##P## and walking ##t## steps of size ##v## in the direction of ##\vec v##, then turning to the direction of ##\vec w## and walking ##s## steps of size ##w## in that direction.

In maths that is: ##Q=P+t\vec v + s\vec w##

Concrete example - (x,y)=(1,-1)+t(3,4)+s(1,0) tells you how to get to point (x,y) from point (1,-1) using (3,4) and (1,0) as cardinal directions.

i.e. you want to get to (x,y)=(8,8), then t=2 and s=1
so you must travel 10 units along the hypotenuse of the 3-4-5 triangle, then 1 unit parallel to the x-axis.

Thanks. That cleared it up. I had never thought of Q like that, but it really helped.
 
  • #4
No worries.
Similarly the parametric equation for a line is ##Q=P+s\vec v## and for a 3D volume you need three parameters.
It gets more fun when you use surfaces instead of planes - those are allowed to curve.
 

FAQ: Parametric Description of a Plane

1. What is the parametric equation of a plane?

The parametric equation of a plane is a set of equations that describes the position of all points on the plane in terms of two independent variables, typically represented by the variables u and v.

2. How is the parametric equation of a plane different from the standard equation?

The standard equation of a plane is in the form Ax + By + Cz + D = 0, where A, B, and C are the coefficients of the variables x, y, and z, and D is a constant. The parametric equation, on the other hand, uses two independent variables u and v in place of x and y, and the equation is written in vector form as P(u,v) = a + ub + vc, where a, b, and c are vectors that represent a point on the plane and its direction.

3. How do you graph a plane using parametric equations?

To graph a plane using parametric equations, you can first choose values for u and v, and then use the parametric equations to find the corresponding values for x, y, and z. Plot these points on a three-dimensional coordinate system and connect them to create the graph of the plane.

4. Can the parametric equation of a plane represent any plane in three-dimensional space?

Yes, the parametric equation of a plane can represent any plane in three-dimensional space. This is because the parametric equation allows for more flexibility in describing the position and orientation of the plane compared to the standard equation.

5. How do you convert a standard equation of a plane to parametric form?

To convert a standard equation of a plane to parametric form, you can choose arbitrary values for u and v and then solve for x, y, and z in terms of u and v. This will give you the parametric equations for the plane. It is also possible to directly convert the standard equation to parametric form using matrix operations.

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