# Plane Frame Normal Orientation Beams

So I have a more theoretical question, which is driven by a more specific question. I will attempt to describe both.

1st theoretical. If you have a line is space that is sloping in two directions, and you use the perp. frame component by default how does it determine the x and y axis? Since it’s a line seems like there is many different solutions.

1. What this is being driven by. So I am using grasshopper to create some beams in Tekla and I want align with the specific surface. What I am not sure of is when I create the beams in Tekla it has determined a specific normal direction for the beams, where the x-axis is along the curve, which is fine. My thinking is that all I need to do is calculate the angle from what Tekla thinks is y-axis and surface normal and I have my the rotation value I need.

What I can’t figure out though is how Tekla by default determined what the beam normal is? I would have figured it would have been along on of the perp. frame axis in grasshopper but it’s not. I also checked Revit it they did the same thing as Tekla for the default beam normal. So whatever these programs are doing it seems to be consistent.

I just need to be able to duplicate it in grasshopper in order to calculate the need rotation.

Normal Direction Test.3dm (406.4 KB)
Normal Direction Test.gh (15.6 KB)

To add to this if I create a plane with the x-axis along the curve and the y-axis with the default then I still don’t get the same direction as what Revit/Tekla do.

In Tekla Structures :
If the line is not vertical*, then Y is aligned to world Z.
If the line is vertical*, then Y is aligned to world Y.

In Grasshopper, I thought this was the same but it seems to be more random/complicated…

However to answer your 2nd question, in Tekla Structures Live Link, you have a wonderful component called `Beam Rotation` that will calculate the the angle you have to feed into the `Position` component, assuming you can provide it the normal vector (of your surface, in your case).

*vertical in Tekla is evaluated as : the projection of the beam axis on XY plane is contained in a 1mm x 1mm square

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Thanks the beam rotation component works great. I didn’t realize that it what it did. Also thanks for other info.

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