# how to know that the point is intersect with the mesh?

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• Aug 21st 2010, 08:29 AM
siteq
how to know that the point is intersect with the mesh?
hello friends...i'm new here...

i have a problem in determining the mesh that intersect with the point...
i have 1 point and 2 mesh...

i have tried many times searching in the google, but it doesn't work...

i hope anyone here can help me to solve my problem..??

thank you...(Happy)
• Aug 21st 2010, 07:10 PM
ojones
Give more mathematical details.
• Aug 21st 2010, 10:45 PM
siteq
opss..sory2x..

i give an example..
if i have 2 points P0 = (2,-3,1) and P1=(-5,4,-3) and
2 planes Plane1 => 4x-2y+2z=5 and plane 2 => 5x-3y-6z=10

my question is, what is the condition that i can used to select which planes is intersect with P0?

thank you...
• Aug 21st 2010, 11:34 PM
yeKciM
Quote:

Originally Posted by siteq
opss..sory2x..

i give an example..
if i have 2 points P0 = (2,-3,1) and P1=(-5,4,-3) and
2 planes Plane1 => 4x-2y+2z=5 and plane 2 => 5x-3y-6z=10

my question is, what is the condition that i can used to select which planes is intersect with P0?

thank you...

did you mean that you need to know how does you can see which plane have (any) points (P_1 pr P_0) ?

$\alpha : 4x-2y+2z=5$

$\beta : 5x-3y-6z=10$

and you need to know is it $P_0(2,-3,1) \in \alpha$ or is it $P_0(2,-3,1) \in \beta$ ? ? ?
• Aug 21st 2010, 11:51 PM
siteq
nope..

actually i have 2 types of planes, and these planes are formed from a triangular mesh..

type 1 : original planes with 18 triangular meshes
type 2 : simplified planes with 16 triangular mesh

what i want to do is, to find the normal distance between the original planes to the simplified planes . and my lecturer give me a clue.
i need to find distance from the points (from original planes) to the simplified plane , and the simplifies plane must intersect with normal line(from original planes)..

i hope my explanation can help u...thank you very much..
• Aug 21st 2010, 11:56 PM
ojones
Siteq: I'm not familiar with the notion of a mesh. What subject is this coming from and can you define it?
• Aug 22nd 2010, 12:06 AM
siteq
calculus vector...

its okat ojones..actually i just want to know...

if we have 3 points P0, P1 and P2, and we have 2 planes PLANE_1 and PLANE_2.

is there any condition that i can used to determine that the normal line from P0 is intersect to PLANE_1 OR PLANE_2 ?
• Aug 22nd 2010, 12:23 AM
Vlasev
Can you post the actual question that you have been given?
• Aug 22nd 2010, 12:23 AM
yeKciM
line can't be "normal" to the point P_0 ....

but to be normal to the any plane there is condition...

if you have (make) line :

$\displaystyle \frac {x-x_1}{m}= \frac {y-y_1}{n}=\frac {z-z_1}{p}$

and plane

$Ax+By+Cz+D=0$

than you have vectors

$\vec{q}=(m,n,p)$

$\vec{n} = (A,B,C)$

and from basic of vectors you have 2 conditions :D (to be parallel or orthogonal)

$Am+Bn+Cp=0$

$\displaystyle \frac {A}{m}=\frac {B}{n}=\frac {C}{p}$
• Aug 22nd 2010, 12:34 AM
siteq
ahaa..ok2x..i know how to get m,n and p...but then, u stated there

Am + Bn + Cp =0 is this the condition for these 2 vectors become parallel and
A / m = B / n = C /p for these vectors become orthogonal ??
• Aug 22nd 2010, 12:43 AM
ojones
Siteq: There's no such thing as a normal line to a point. You're not forming your question clearly I'm afraid.
• Aug 22nd 2010, 12:50 AM
siteq
aha..actually that one i just copy from my lecturer..maybe 'normal' thanat she mean in her email is the normal from the plane..i'm sorry for that...i miss understood...my mistake...

maybe the correct is, the normal plane to a point.....
• Aug 22nd 2010, 12:55 AM
yeKciM
Quote:

Originally Posted by siteq
ahaa..ok2x..i know how to get m,n and p...but then, u stated there

Am + Bn + Cp =0 is this the condition for these 2 vectors become parallel and
A / m = B / n = C /p for these vectors become orthogonal ??

there is one vector attitude that goes like this : "two vectors are orthogonal if their scalar product is zero". .. meaning that $(\vec{x}, \vec{y}) =0$ ...

Quote:

Originally Posted by siteq
aha..actually that one i just copy from my lecturer..maybe 'normal' thanat she mean in her email is the normal from the plane..i'm sorry for that...i miss understood...my mistake...

maybe the correct is, the normal plane to a point.....

again normal to point... :D:D:D look, nothing line or plane can be normal to point... try imagine that in your head or draw it for yourself ... you have point in space and how do you think you should position line (or plane) so that it will be normal to point :D:D:D:D

P.S. and please give exact question which you got ... so there will not be any more misunderstanding :D
• Aug 22nd 2010, 05:50 PM
siteq
the exact question is not in english...and that's why i cannot put it here and i need to translate into english and then it become missunderstanding...heehee..
• Aug 22nd 2010, 06:23 PM
yeKciM
Quote:

Originally Posted by siteq
the exact question is not in english...and that's why i cannot put it here and i need to translate into english and then it become missunderstanding...heehee..

try giving it to someone who will be able to translate it for you :D
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