Particle Orientation

[NVP]

How  is Particle Orientation calculated? In NI Vision Concepts Manual the forumla is given as Tan invese of(2 * SumXY - (SumXX - SumYY)).  This formula seems to be wrongs. As SumXY is never going to be zero, so how do we get an Orinetation of angle '0'. ? What is the correct formule??

[risheeb]

Hi NVP,

It seems that there is an error in the equation as it appears in the Vision Concepts Manual.  The values of that are used to calculate the angle are not the summations, but the moments of inertia about each axis.

The way I figured this out was using the "Particle Orientation" example in LabVIEW.  I used the IMAQ Particle Analysis VI in this example to pull out different properties for each particle.  I found that if I used Ixy, Ixx, and Iyy in place of the summations in the equation, I was able to calculate the angle properly.

I will pass on this documentation error so that it will be corrected in future versions of the Vision Concepts Manual.  Thanks.


Rishee B.
Applications Engineer
National Instruments

[NVP]

Hi,

Even i tried calulating manually. I got the right answers when i used moments instead of Sums.

 It would be more helpful for the user if all the special cases are also mentioned in the Vision Concepts Manual. (For Example : How is Angle 0 & Angle 90 obatined, when a rectangle is rotated by 90 degree as we have the numeretor being 0 for both the cases? The solution is that the sign of the denominator is considered. I feel special cases like this also should be mentioned wherever necessary.

Thanks!!