Lay Flat

A lightweight and efficient Blender add-on that perfectly aligns and rests any 3D object on the ground (XY plane, where Z=0) based on a selected face. This is particularly useful for 3D printing preparation, architectural visualization, or anytime you need an object to sit completely flush against a surface.

Usage Guide

1. Select Object: In the 3D Viewport, select the mesh object you wish to lay flat.
2. Enter Edit Mode: Press Tab to switch into Edit Mode.
3. Select Face: Select the specific face that you want to act as the bottom of the object (the face that will rest on the ground).
4. Open Sidebar: Press N to open the Sidebar menu on the right side of the 3D Viewport (if it isn't already open).
5. Run Tool:
   • Locate and click the Lay Flat tab on the right edge of the Sidebar.
   • Click the Lay Flat button.
   • Alternatively, you can press F3 to open the search menu, type "Lay Flat", and select the operator.

The object will instantly be rotated and moved so that the selected face sits exactly flush against the Z=0 plane!

Technical Details (How it Works)

For developers and advanced users, the script performs the following mathematical transformations securely via Blender's mathutils:

1. Normal Extraction: It extracts the selected face's normal and center point.
2. Global Space Conversion: It converts the local normal into global space, utilizing the transposed inverse of the object's 3x3 world matrix. This ensures the calculation remains robust even if the object has been non-uniformly scaled.
3. Rotation Calculation: Calculates the quaternion rotation required to align the global face normal directly downwards toward (0, 0, -1).
4. Transformation:
   • Translates the object so the face center moves to the origin.
   • Applies the newly calculated rotation matrix.
   • Translates the object back to its original X and Y coordinates, whilst snapping its Z coordinate exactly to 0.0.
5. Matrix Application: Safely overrides the object's matrix_world all in a single step for optimal efficiency and precise floating-point behavior.