What if? POP group

[stig_olsen]

Hi,

 

I have some particles that I want to group based on how fare they have reached down the Y-axis.

In H12 I used the $TY < -5 -expression to say that it should group when the particles had fallen to under Y-5.

 

Im a newbie so I dont understand the new POP Group, and my old expression doesnt work.

 

I really appreciate your help!

 

All the best, Stig Olsen

[j00ey]

You can use the expression 

 

ingroup = @P.y < -5;

 

see attached hipnc

pop_group.hipnc

[stig_olsen]

Thank you!!

How does that VEX expression really works? Why write ingroup, why use the @ and what does P.y stand for?

 

Stig

[magneto]

You can also use setpointgroup function I think. But ingroup is easier in this case. @ is for binding to the attribute and P.y is the Y coordinate of point/particle position. You can also do P[1] if you want.

[j00ey]

Just to clarify, P - referring to position - is a vector and y refers to the second component of the vector. The reason P[1] also works is that the components are numbered starting at 0 so P[1] is the second component of the vector P.

 

A good way to learn some very useful vex snippets is if you look in the little dropdown arrow to the right of the text box, there are some presets in there. Most, if not all, of the vexpression text boxes have them.