angle between two objects approximated as lines

[Biswa]

Hi there,

I have NI Vision and have been wondering the best way to get the angle of two objects that has been approximated by a line (say using edge detection). I have attached one frame of the avi file for your perusal. The scene is changing from frame to frame where the objects are constantly being shifted and rotated. I can track either the small object or the big object in isolation using pattern matching algorithms but the issue lies in moving the edge detection rake from frame to frame for two objects in a single trial. Please advise.

Cheers, B.

[Biswa]

In the attached image I would like fit a line on the leg of the image and another line on the spike coming out of the leg and get an angle between the two. The present image has been convereted from color to grayscale with a power (3.5) look-up table filter.

[K_Bull]

Hi,

You can do this in several ways. The straight forward way would be to use the trigonometric funtions. If you filter the image you are acquiring to get the co-ordinates of the edges of the stick and also the refence to ground, as shown in the image attached, you can use the known values to calculate the angle the stick is aligned to ground.

Here, treat the picture as a 2D image, get the x,y co-ordinates of the point of interception (C) and the co-ordinates of a point in your stick (A). The difference in value of y between A and ground is your "p" and the difference in value of x between C and x value of the point (A) is your "b". Use the supplied equation to work out the angle as shown in image.

This should get you started and hope it helps.

Regards,

[K_Bull]

Hi,

Thought this page contains some relative information about - What Algorithms Does the NI Vision Software Use?
Hope this helps.

Regards,