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Image Processing using concentric rake



I am doing a college project using Labview 2010 and a webcam to capture an image and process it. I am trying to find and measure a line in a circular region of interest.There are two circles bounding my search region, an inner circle (the origin) and the outer circle ( the edge of my image) as of now I am able to track and measure both them. My plan was to use these measurements to set the Contours for both of the individual shapes that define an ROI but I am unable to do so. I have attached a VI that I have been working on aswell as a sample of an image. 

Also once I get this problem sorted out  I would eventually like to be able to set the ROI for the Rake tool automatically by using the measurements acquired from the find circle tools.

Thank you very much in advance.


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Hello darrencgray,


Thank you for supplying sample images.  I am currently looking at how the two circles can be detected, and then converted into a region of interest. 


The VI you have supplied seems to be a combination of your own work within Vision Assistant, which was then used to auto-generate LabVIEW code.  Please confirm whether this is the case, so I can know if which environment to try and improve your application in. 



George T.
Senior Applications Engineering Specialist
National Instruments UK and Ireland
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Hi Darren,


To measure the "line", maybe you don't even need to setup the ROI. Have a look at my Vision Assistant script, it carries out a simple measurement of the line length.

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Hello GT 3000


Yes I did use NI Vision to detect the two circles and then I attempted to connect the results of both tools to the concentric rake tool. I have made further attepmts since I posted the last message. I was trying to create my own ROI descripter by extracting the centre of aech of the circles and their radi into a cluster but that did not work either.


Thank you for your help



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Hello Vladimir


Thank you for that, it is very helpful and it does work but I am afraid that I also want to calculate the angle of the line.


Thank you

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Hello darrencgray,


I have made a VI that will help you select circles from one of the sample images you have provided.  The code will find two circles and show you their properties.  You will need to mathematical manipulate the circle data into a Region of Interest descriptor for the 'Find Concentric Edge' function. 

  1. Run the VI and watch the Block Diagram with 'Highlight Execution' on.
  2. Draw a Region of Interest around the center circle and click OK.
  3. Draw a Region of Interest around the outer circle and click OK.


The details for each circle is displayed on the front panel.  You will receive an error as the code arrives at the VI called 'Find Concentric Edge'.  This is because you need now replace the sample ROI descriptor with your own numbers. 


If you require more help on how to manipulate cluster data, please see the link below:

Tutorial: Arrays and Clusters


I believe this example and the notes I have added should help you better understand how to setup this vision application.


Best Regards,

George T.
Senior Applications Engineering Specialist
National Instruments UK and Ireland
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Message 6 of 8

Hello gt3000


Thank you very much for the work you have put in, I really appreciate the help. Unfortunately the process of finding the circles in the image has to be automatic and I have that part of the program working already. I have tried to cluster the sizes and the coordinates of each of the circles into the concentric tool but it does not work. I will keep working on it.


Thank you again.

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You can also measure the angle of the line with the particle analysis. Just click "Select Measurements" in the particle analysis step and choose another measurement, "Orientation".

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