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Thread Subject:
homogeneous points

Subject: homogeneous points

From: chee ali

Date: 1 Jan, 2010 15:07:03

Message: 1 of 11

hi,i want 2 ask somthing about homography.i want to calculate homography matrix H,the equation is x’=Hx.
x’ is 3xN set of homogeneous points,now i am not getting the point that how to calculate this 3xN set of homogeneous points.
please give me some idea.i hope you ill rep.

Subject: homogeneous points

From: Jan Simon

Date: 1 Jan, 2010 16:05:04

Message: 2 of 11

Dear chee ali!

> hi,i want 2 ask somthing about homography.i want to calculate homography matrix H,the equation is x’=Hx.
> x’ is 3xN set of homogeneous points,now i am not getting the point that how to calculate this 3xN set of homogeneous points.

I don't get what you want to calculate: The homography matrix or the homogenous points?

Have you read this: http://en.wikipedia.org/wiki/Homography ?

Good luck, Jan

Subject: homogeneous points

From: chee ali

Date: 3 Jan, 2010 18:30:07

Message: 3 of 11

"Jan Simon" <matlab.THIS_YEAR@nMINUSsimon.de> wrote in message <hhl6fg$f1a$1@fred.mathworks.com>...
> Dear chee ali!
>
> > hi,i want 2 ask somthing about homography.i want to calculate homography matrix H,the equation is x’=Hx.
> > x’ is 3xN set of homogeneous points,now i am not getting the point that how to calculate this 3xN set of homogeneous points.
>
> I don't get what you want to calculate: The homography matrix or the homogenous points?
>
> Have you read this: http://en.wikipedia.org/wiki/Homography ?
>
> Good luck, Jan

yes i have read it.and i want to calculate the homogeneous points in matlab.

Subject: homogeneous points

From: Jan Simon

Date: 3 Jan, 2010 20:39:03

Message: 4 of 11

Dear Chee!

> > > hi,i want 2 ask somthing about homography.i want to calculate homography matrix H,the equation is x’=Hx.
> > > x’ is 3xN set of homogeneous points,now i am not getting the point that how to calculate this 3xN set of homogeneous points.
> >
> > I don't get what you want to calculate: The homography matrix or the homogenous points?
> >
> > Have you read this: http://en.wikipedia.org/wiki/Homography ?
> >
> > Good luck, Jan
>
> yes i have read it.and i want to calculate the homogeneous points in matlab.

Ok. Do I understand correctly: you have H and x and want x' ?!
  x2 = H * x;
Does this help?! Or do you want x and have x' ?! Then inspect:
  help slash
Kind regards, Jan

Subject: homogeneous points

From: chee ali

Date: 3 Jan, 2010 23:29:03

Message: 5 of 11

"Jan Simon" <matlab.THIS_YEAR@nMINUSsimon.de> wrote in message <hhqv97$o6u$1@fred.mathworks.com>...
> Dear Chee!
>
> > > > hi,i want 2 ask somthing about homography.i want to calculate homography matrix H,the equation is x’=Hx.
> > > > x’ is 3xN set of homogeneous points,now i am not getting the point that how to calculate this 3xN set of homogeneous points.
> > >
> > > I don't get what you want to calculate: The homography matrix or the homogenous points?
> > >
> > > Have you read this: http://en.wikipedia.org/wiki/Homography ?
> > >
> > > Good luck, Jan
> >
> > yes i have read it.and i want to calculate the homogeneous points in matlab.
>
> Ok. Do I understand correctly: you have H and x and want x' ?!
> x2 = H * x;
> Does this help?! Or do you want x and have x' ?! Then inspect:
> help slash
> Kind regards, Jan

i want to calculate x right.calculation of H is next step.but right now i want to calculate homogeneous point x.and this x is a 3xn matrix.
i have NO idea that how to calculate homogeneous point x.

Subject: homogeneous points

From: Jan Simon

Date: 4 Jan, 2010 08:23:03

Message: 6 of 11

Dear Chee!

> > Ok. Do I understand correctly: you have H and x and want x' ?!
> > x2 = H * x;
> > Does this help?! Or do you want x and have x' ?! Then inspect:
> > help slash
>
> i want to calculate x right.calculation of H is next step.but right now i want to calculate homogeneous point x.and this x is a 3xn matrix.
> i have NO idea that how to calculate homogeneous point x.

You repeatedly tell us, what you want to calculate. But you do not mention, what you have!
x can be calculated, if you have H and x'.
x' can be calculated, if you have H and x;
H can be calculated, if you have x' and x.
It is not possible to "calculate" x *and* H!

It might be the best, if you describe your problem with more details. Please tell us the exact values or definitions, you want to base the calculations on. What are the conditions your x should satisfy?

Kind regards, Jan

Subject: homogeneous points

From: Bc

Date: 23 Mar, 2010 20:39:20

Message: 7 of 11

"chee ali" <chase_the_dawn_2000@yahoo.com> wrote in message <hhl32n$e1d$1@fred.mathworks.com>...
> hi,i want 2 ask somthing about homography.i want to calculate homography matrix H,the equation is x’=Hx.
> x’ is 3xN set of homogeneous points,now i am not getting the point that how to calculate this 3xN set of homogeneous points.
> please give me some idea.i hope you ill rep.

I have a feeling that what you want is to take point from your image using ginput and then used those points for the homography. This would probably mean that you will get the pixel coordinates (xi,yi) for each point and append the 1, to make them homogeneous:

(x1,y1,1)
(x2,y2,1)...

-Bc

Subject: homogeneous points

From: blue ice

Date: 20 Dec, 2010 19:02:08

Message: 8 of 11

"Bc " <bcortez23@gmail.com> wrote in message <hob8tn$9j$1@fred.mathworks.com>...
> "chee ali" <chase_the_dawn_2000@yahoo.com> wrote in message <hhl32n$e1d$1@fred.mathworks.com>...
> > hi,i want 2 ask somthing about homography.i want to calculate homography matrix H,the equation is x’=Hx.
> > x’ is 3xN set of homogeneous points,now i am not getting the point that how to calculate this 3xN set of homogeneous points.
> > please give me some idea.i hope you ill rep.
>
> I have a feeling that what you want is to take point from your image using ginput and then used those points for the homography. This would probably mean that you will get the pixel coordinates (xi,yi) for each point and append the 1, to make them homogeneous:
>
> (x1,y1,1)
> (x2,y2,1)...
>
> -Bc


is it possible to warpe two images after calculating homography without using ransac????if yes than how

Subject: homogeneous points

From: blue ice

Date: 20 Dec, 2010 19:02:08

Message: 9 of 11

"Bc " <bcortez23@gmail.com> wrote in message <hob8tn$9j$1@fred.mathworks.com>...
> "chee ali" <chase_the_dawn_2000@yahoo.com> wrote in message <hhl32n$e1d$1@fred.mathworks.com>...
> > hi,i want 2 ask somthing about homography.i want to calculate homography matrix H,the equation is x’=Hx.
> > x’ is 3xN set of homogeneous points,now i am not getting the point that how to calculate this 3xN set of homogeneous points.
> > please give me some idea.i hope you ill rep.
>
> I have a feeling that what you want is to take point from your image using ginput and then used those points for the homography. This would probably mean that you will get the pixel coordinates (xi,yi) for each point and append the 1, to make them homogeneous:
>
> (x1,y1,1)
> (x2,y2,1)...
>
> -Bc


is it possible to warpe two images after calculating homography without using ransac????if yes than how

Subject: homogeneous points

From: blue ice

Date: 20 Dec, 2010 19:03:06

Message: 10 of 11

"Bc " <bcortez23@gmail.com> wrote in message <hob8tn$9j$1@fred.mathworks.com>...
> "chee ali" <chase_the_dawn_2000@yahoo.com> wrote in message <hhl32n$e1d$1@fred.mathworks.com>...
> > hi,i want 2 ask somthing about homography.i want to calculate homography matrix H,the equation is x’=Hx.
> > x’ is 3xN set of homogeneous points,now i am not getting the point that how to calculate this 3xN set of homogeneous points.
> > please give me some idea.i hope you ill rep.
>
> I have a feeling that what you want is to take point from your image using ginput and then used those points for the homography. This would probably mean that you will get the pixel coordinates (xi,yi) for each point and append the 1, to make them homogeneous:
>
> (x1,y1,1)
> (x2,y2,1)...
>
> -Bc


is it possible to warpe two images after calculating homography without using ransac????if yes than how

Subject: homogeneous points

From: blue ice

Date: 20 Dec, 2010 19:03:07

Message: 11 of 11

"Bc " <bcortez23@gmail.com> wrote in message <hob8tn$9j$1@fred.mathworks.com>...
> "chee ali" <chase_the_dawn_2000@yahoo.com> wrote in message <hhl32n$e1d$1@fred.mathworks.com>...
> > hi,i want 2 ask somthing about homography.i want to calculate homography matrix H,the equation is x’=Hx.
> > x’ is 3xN set of homogeneous points,now i am not getting the point that how to calculate this 3xN set of homogeneous points.
> > please give me some idea.i hope you ill rep.
>
> I have a feeling that what you want is to take point from your image using ginput and then used those points for the homography. This would probably mean that you will get the pixel coordinates (xi,yi) for each point and append the 1, to make them homogeneous:
>
> (x1,y1,1)
> (x2,y2,1)...
>
> -Bc


is it possible to warpe two images after calculating homography without using ransac????if yes than how

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