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Contradictory Logic When Combining Rules In Group Sops


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Just posted the attached to SESI support to ask if it is a bug but it is interesting so I thought I'd post it here too.

It looks like the Group SOP supports combining rule types but unfortunately sometimes it ADDs rules and other times it uses OR logic. Check out the attached example to see what I mean. The groups animate if you press play.

In both group SOPs I enable both a number rule and a bounding rule. In one group the number rule is a group by range and this clearly uses AND logic to group. In the other group the number rule is an expressions and this uses OR logic.

I think the ADD logic makes the most sense which is what you get when you use the group by range option.

Of course you can work around it by splitting the grouping into seperate groups and then using the combine tab in another Group SOP to get the rule you want.

John

groupCombinationBug.hip

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It looks like if you check "Create Ordered" toggle, the range_plus_bounding___WORKS_LIKE_AN_AND Group SOP works as an OR as expected. Not sure why it should be checked though...

lll

That's odd!!! When I try toggling in "Create Ordered" it isn't doing an AND or an OR it is simply switching off the bounds logic. I think it is another bug!

Actually, I think the Group SOP you mention here is working correctly (with the "Create Ordered" disabled) as it combines the grouping logic under both options. It's the other Group SOP that looks buggy to me.

As to why the points selected should change when "Create Ordered" is toggled this isn't a feature I've used before but it sounds form the help that it should just change the order of the points listed in, say, the pointlist expression. It really shouldn't be changing the set of points returned unless I'm misunderstanding it. As I said, I think it is a bug.

john

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Well, I have always felt a bit confused when understanding math logic rules since math analysis classes (somehow I perceive this logic different to what some manuals state).

Thinking about range_plus_bounding___WORKS_LIKE_AN_AND Group SOP - isn't OR logic supposed to choose either points from 0-$N or in bounds points (i.e. choose points from both rules)? Isn't it what it does, when the toggle is switched?

In any case you are probably right that something is wrong with the Group SOP. What do SESI say?

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Thinking about range_plus_bounding___WORKS_LIKE_AN_AND Group SOP - isn't OR logic supposed to choose either points from 0-$N or in bounds points (i.e. choose points from both rules)? Isn't it what it does, when the toggle is switched?

In any case you are probably right that something is wrong with the Group SOP. What do SESI say?

Hi MADjestic,

With Create Ordered enabled the range_plus_bounding___WORKS_LIKE_AN_AND Group SOP is just using the Number rule (i.e select so many points out of 200).

The two rules in the range_plus_bounding___WORKS_LIKE_AN_AND Group SOP are

1) NUMBER RULE - select $F points out of 200

2) BOUNDING RULE - select all of the points inside the bounding sphere

If AND logic is applied the rule is select only the points that are in the number range AND those also inside the sphere. This is indeed what happens with the "Create Ordered" toggle switched off and in my mind is correct.

If OR logic is applied it should select those points in the number range OR the points inside the bounding sphere. All of the points inside the sphere would be selected at all times. However when "Create Ordered" is toggled on the points inside the bounding sphere are only selected if they obey the range rule. In other words, the sphere rule is being completely ignored with the toggle on! Very odd.

I haven't heard back from SESI yet. I'm hoping they don't say that multiple enable toggles shouldn't be used because if that's the case why did they desgin the Group SOP to allow multiple rules to be enabled?

john

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