https://mods.factorio.com/mod/entity-symmetry
https://github.com/sparr/factorio-mod-entity-symmetry
Places rotated/mirrored entities around specified points.
The purpose of this mod is to speed up development of blueprints, particularly for rail junctions.
Usage
Craft a "Symmetry Center" item. Place it in the world as a "Symmetry Center" entity. Place some entities nearby and see them duplicated around the center. Remove those entities and the duplicates will be removed.
Configuration
The Symmetry Center entity is a constant combinator. Setting signals within it will control its behavior as follows:
C
Move the center of symmetry to a corner/edge of the tile. 0 = north edge, 1 = northeast corner, ..., 6 = west edge, 7 = northwest corner.
D
Set the max distance from the center to copy entities. Default is 64. Negative numbers are circular distance, positive square.
R
Rail entities are always placed on a 2x2 grid. This setting controls whether other entities honor that grid. -1 is never. 1 is always. 0 is not until a rail entity is placed then it automatically becomes 1.
M
Mirroring instead of rotational symmetry
X
Mirroring axes. 0 = neither, 1 = X, 2 = Y, 3 = both.
S
Degree of rotational symmetry. Default is 4, 2 is also useful. Other numbers are pretty but not practical.
item
Positive signal will copy only the signaled item(s). Negative signal will exclude the signaled item(s) from copying.