Geometry Nodes: rotational alignment of objects with reference to other object

Question

I want to achieve the following: I have a more or less complex but flat mesh without much details representing the hull of an office building. I want to add details like windows, blinds and other structures by using geometry nodes (maybe there are other ways, but I use this as well as a project to learn a bit about GNs). Up to now I managed to place a grid at the hull where the grid instances are aligned to faces' normals by the help of the "Align Euler to Vector". As a more simple example see the screenshot of the same node setup applied to a cube: The cube represents the hull of the building, the little rectangles at the faces of the code will be the instances of a prototype window in the future. The corresponding node setup looks like this: Wheat is wrong in this setup is the alignment of the rectangles at the "x" faces (red axis) which are upward where I want to have them horizontally rotated.

How can I achieve this?: rectangular prototype "window" aligned to cube face normals and all oriented horizontally on x/y faces.

File with cube and node setup: Blender file on MS OneDrive

Answer 1

it might not be the cleanest and cleverest node setup, but it works:

result:

Answer 2

I found the/an answer by myself:

• The "Align Euler to Normal" can be thrown out
• A "Rotate Instance" node allows to rotate previously instanced objects
• By using the "Compare" node, I can generate an "if (normal = x-axis)" statement filtering the instances
• The rotation of instance object is only executed where the "IF" is TRUE:

Result:

Note that I changed the option of the "Transfer Attribute" node from "Nearest Face Interpolated" to "Index" (which did not make a difference in my example here...)

With the help of this (and a bit more for sure), I managed to create windows, window reveals and little "balconies" above the windows of my building:

As handle for the geometry nodes I use a horizontal "ribbon" following the building contour.