Angle value in results of IMAQ Find Straight Edges 3 VI

[goodbooroondook]

Hello everyone,

I'm working on a project for automated machine vision system using NI Vision.

One of the tasks is detect straight edge of the object. So, I'm using IMAQ Find Straight Edges 3 VI and I have question about results of this function.

For example, if I set method type of the detecting edge to "First Edge Rake" - function return explainable results, which are consistent with function description. But, if I set method type to "Hough Edge Rake", function returns strange value of edge angle. Moreover, if I make a little change in orientation settings, function returnes the same edge, but the differ angle in results.

So, could anybody explain what angle returned using Hough Edge Rake method? 

[goodbooroondook]

Thanks everyone for the help,

I found solution. Sorry for a long response.

So, for Hough Edge Rake method: angle value in results is returning relatively to expected orientation of line. For others methods - relatively to image axis.

You can use this code sample to fix results for uniform representation.

[goodbooroondook]

Another question is "Min. Points (%)" parameter. In description said: Min. Points (%) specifies the minimum number for points as a percentage of the number of search lines that need to be included in the detected straight edge. The default is 25%.

But, this parameter works only for Hough Edge Rake method 😉

For example, If I set First Edge Rake (0) method, function can return line based on less number of points, than assigned in Min. Points (%) parameter.

So, it would be wonderful, if NI will carefully check and update description for their functions of NI Vision Development Module.