Grasshopper

algorithmic modeling for Rhino

Hi

These series of post is dedicated to rarely used components... but maybe one day they could be useful, if only you know how they works!

This post is about Relative Item and Relative Items: if you ever used one of these in your works and you would like to contribute with examples or hints, you are in the right place.

Thanks

Paolo

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The purpose of Relative Item[s] is to select pairs of items from one or two datatrees respectively. You specify the pairing via an offset mask, which looks like path/item notation except that the values in it are meant to be added to the existing item location.

I realise the above explanation is pretty opaque... Consider the example, if we want to create those zigzag lines, what we in effect want is to create lines between every point, and the corresponding point in the next branch over. So point0 in branch0 gets connected with point0 in branch1, point0 in branch1 gets connected with point0 in branch2, etc. It's the same story for point1 in branch0, it gets connected to point1 in branch1.

The offset pattern for this case looks like {+1}[0], meaning: go to the next branch {+1}, but keep the same item index [0].

This precise mapping can also be achieved using Flip Matrix, but Relative Items allow you to be more specific about exactly which items should correspond, and it allows you to wrap the correspondence back to zero, which is useful if the grid had been on a cylinder instead of a flat plane, because then you actually want to connect the last values back to the first ones.

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So one may say that its function is a bit like shift list but in multidimensional trees. 

Its like stopping using graft and move to path mapper in some trees, isn't it? ;-)

Ok. pretty clear. I have to find out some time to test this one.

I thought this was a useful example (also by David of course...)

http://www.grasshopper3d.com/forum/topics/spiral-3

Sure! Thanks

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