How to find the coordinates of the four corners of a quadrilateral in an image?

[Ian_Ren]

Can anyone share some ideas on

1) how to detect the four coners of a quadrilateral in an image using the image/vision tool in LabVIEW?

2) how to extract sub-area of an image to create a new image?

3) how to convert an image to a 2D array?

Thanks.

Ian

[Kevin_F]

Hey Ian,

Finding the corners of a quadrilateral isn't trivial but I think you will be best served with the geometric matching functionality of the vision assistant. Check out this example:http://zone.ni.com/devzone/cda/epd/p/id/5555 and this one:http://zone.ni.com/devzone/cda/epd/p/id/5532.  I also think the Rectangular Target processing example in the FRC shipping examples (Help->Find Examples-FRC2012->Vision).

You can use ImaqExtract to get sub area of an image - you can provide it the region of interest and then specify to keep every row if you don't want to decimate the image.

This example shows how to convert an image to a 2D array:http://zone.ni.com/devzone/cda/epd/p/id/5679