Transferring data between different objects in / using Geometry nodes

Question

Transferring data between different objects in Geometry nodes

I know we can use the Object info node to get the geometry data from another object and use the geometry data but what about a specific data field.

Example: I'm trying to transfer the float data of the inner radius of object 1 to object 2 outer radius

Data to be taken from object 1 (inner hole radius).

Data to be transferred to object 2 (Outer hole radius).

What I've tried.

I can see the rt_rad attribute created

But how do I get the second object to access the Named Attribute. A link seems to be missing.

Attached file.

Answer 1

When you create a new geometry using "Primitive" nodes, you're asked for values describing those objects, like a cylinder radius. Those are single, constant values, because each such node is creating a single object, for which only a single value makes sense: a cylinder has only one radius.

However, you try to transfer that value from an attribute array, which stores multiple values, one for each element of the attribute's domain. In order to get just one, you can use an attribute statistic node:

With this technique, typically it doesn't matter if you use min, max, mean or average output of the Attribute Statistic node. However in your case you're joining multiple geometries, some without the named attribute, which then is set to default 0 upon joining - so I decided to use the max.

Answer 2

You don't need to use the Attribute Statistics-Node to retrieve a named attribute of different objects like Markus von Broady suggested.

1. Accessing attributes with Geometry-Nodes

Actually it is better to use the "Sample Index"-Node instead as shown in figure below, cause it does no aggregation-calculations on the whole domain, which can be pretty large.

2. Accessing attributes with Python

If you need to retrieve the value of the named attribute in your Python script you have to do it via the evaluated object in conjunction with its dependency graph :