roipoly

Hi,

I would like to know if it is possible to create a ROI on a current figure.

 x=[1 2 3 4 5 6];
 y=[7 8 9 10 11 12];
 plot(x,y)

Now i would like to define a ROI, is it possible to use roipoly

 I='Figure 1'
 r=[-20 20]
 c=[-20 20]
 BW=roipoly(I,r,c)

cheers

nicolas

Answer 1

[Image Analyst]

No. I has to be an image, not a string. And r and c must have at least three points - that would be a triangle. As you have it, r and c define a line, not a polygon.

[Nicolas]

sorry, i wrote something quick.

actually my polygon is 13 points.

I'm looking for creating a ROI, because I want to analyze that particular ROI using voronoi rather than the whole figure or image. And I haven't found so much information on the subject.

[Image Analyst]

I don't know what that means. How can you analyze a region using a Voronoi diagram?

[Nicolas]

I don't know neither. My idea was to calculate the area of the polygon generated using voronoi within a defined area. It seems I missed something in the understanding of how voronoi works.

[Walter Roberson]

Voronoi diagrams... aren't they the ones that go to infinity at the edges?

[Image Analyst]

Why don't you just post your image to tinypic.com and tell us what you want to measure it it, rather than think up some random algorithm and see how it might be applied to your image?

[Nicolas]

in exemple 2 of the help for "voronoi", the figure shows that not all the lines are infinite... i'm confused.

[Image Analyst]

No, not all are infinite. But those that intersect the edges would go to infinity if they didn't get clipped by the edges of the diagram. Anyway, what do you think you want to do with the voronoi? Or better yet, what do want to do in your ROI?

[Nicolas]

in my ROI, I have a population of points that increase with time, for each new point i want to recalculate the Voronoi and study the evolution of the polygon areas for each point.

[Walter Roberson]

It sounds to me like you should be working in the dual space from voronoi, namely the delaunay triangulation.