# What exactly decides if two primitives are connected?

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Posted (edited)

This cube has only 14 points. The top half and the bottom half share the same middle points. However, Connectivity SOP still considers it has two pieces in primitive mode.

1. Why? What decides whether two primitives are connected or not? Intuitively, if two prims share any point, they are connected... but Houdini doesn't think so.

2. How to make it a connected piece?

Please take a look at the attachment.

Edited by raincole

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After boolean in the middle edge you have double points. There is two separate pieces

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Posted (edited)
41 minutes ago, tamagochy said:

After boolean in the middle edge you have double points. There is two separate pieces

The double points are removed by Clean SOP already and there is no double point anymore. That's exactly why I asked this question.

Edited by raincole

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Better give a scene. Will be easy to understand.

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The connectivity SOP use the name attribute created by the booleanfracture.
Delete this attribute and you can see than the connectivity will no longer consider the cube as two separated pieces.

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Posted (edited)

It seems, that two prims are connected, if they share a same point (this is less restrictive than sharing an edge). If you want the edge only case you can use the divide sop (dual graph).

In your case, clean sop is fusing the points, which makes the geometry connected, if you turn it of (clean sop) you will get two classes and you see, that there are duplicated points (show point numbers).

explodeview is just using the name attribute and breaks the points again.

connectivity_prims.hipnc

Edited by Aizatulin

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12 hours ago, Aizatulin said:

It seems, that two prims are connected, if they share a same point (this is less restrictive than sharing an edge). If you want the edge only case you can use the divide sop (dual graph).

In your case, clean sop is fusing the points, which makes the geometry connected, if you turn it of (clean sop) you will get two classes and you see, that there are duplicated points (show point numbers).

explodeview is just using the name attribute and breaks the points again.

Thank you very much. I thought explodeview checked the connectivity, but it actually, as you said, checks name attribute.

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