find circle radious

[cloe]

Hi, I'm new of Labview Vision Tool.

This is my application: I've a road tunnel in which there's a fire. I want to calculate the distance between the fire and my thermocamera.

This is my idea (I hope it is a good idea ) 😞 the ceiling above the fire is hot, so I see a part of circle like in the image (see the green line).

If I have the radious of this circle (with "find circles") I can draw the distance between camera and fire.

I think that the big problem is to obtain the binary image. You think is better work on colours or temperature?

how would you do?

thank's a lot

Message Edited by cloe on 03-10-2008 10:21 AM

[BruceAmmons]

This looks like a pipe dream to me.  I don't see any way to analyze your image and get what you want.  Sorry.

I would consider looking at a rangefinder or some other piece of equipment instead of using vision.

Bruce

[Yuri33]

I've had to extract circles from crappy images before (pupil of an eye using a low contrast, low brightness setup).  It can be done, but you're going to need a much broader vew of the ceiling outline to get a decent circle.  With only the section you've shown, your circles will be all over the place.  In my experience, you need at least half the outline of a circle to find a consistent fit.  The first step is probably to back up your camera so that more of the ceiling outline can be detected.  If the fire is only able to heat up that small section of the ceiling, then you're probably out of luck.

[cloe]

thanks for your suggestions. I had already read your post on the pupils of the eyes. 
the logo is not a problem because the image that I get with labview doesn't have the logo, but it is a function z=f(x,y) with z=temperature.  
I believe that it is important possession an image with the defined contours. then I can make a treshold on the temperatures, or to work on the hulling and brightness of the colors. 
my problem is to succeed in isolating well the circle of the ceiling: in base to the ua experience is better to work on the colors or on the temperature? 
thanks

[BruceAmmons]

It would be easier to work with the temperatures instead of the colors.  The temperatures are a grayscale image, which is always easier to work with than color images.

Perhaps with a clearer image you can do more.  It still looks difficult to me.  Also, it doesn't look like the arc you highlighted is a circle - it looks more like an oval.

Bruce