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What are some good implementation of efforts to digitise an analog dial?

asked 2012-10-05 02:29:48 -0600

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For example,

I want to install a camera in front of the dial and from the received images, extract the information like time in watch or Force from UTM.

This data extraction has to happen in Real-time and continuously. So, for example, the program output should be "the time" read from the watch which updates say, every second.

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I was thinking, first to convert the video to images by reducing the frame rate to say one per sec, then extracting the dial from the image, and read the angle of the pointer (blue) from the images, then convert the angle to corresponding force value by calibration.

chintanp gravatar imagechintanp ( 2012-10-05 02:35:36 -0600 )edit

Is it possible to extract the angle without converting to images?

chintanp gravatar imagechintanp ( 2012-10-05 02:36:12 -0600 )edit

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answered 2012-10-05 02:40:38 -0600

elmiguelao gravatar image

updated 2012-10-05 07:51:57 -0600

You can use the Hough transform to detect straight lines in the frame. Once the main lines are found, and seems it would work pretty good according to your second picture, the angles can be postprocessed. Note that the Hough operation ("transform") will return loads of straight lines of different lenght in the picture, unwanted ones should be filtered out via line size.

There is this full tutorial in openCV with code included:

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Saying that hough transform is the same as findContours is a bit confusing, what do you mean by that?

Rui Marques gravatar imageRui Marques ( 2012-10-05 06:43:46 -0600 )edit

True, now that I read that. I just meant that cvFindContours also will find loads of contours that a human eye would not find relevant. I will edit the answer.

elmiguelao gravatar imageelmiguelao ( 2012-10-05 07:51:11 -0600 )edit

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Asked: 2012-10-05 02:29:48 -0600

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Last updated: Oct 05 '12