The Citrine Citadel


Slotifier is a simple program which takes an Excellon drill file input, searches for overlapping drill hits, and generates a new drill file with those hits converted to a single slot (G85 entry in the drill file).

This is useful when using a PCB tool which does not generate such slots directly, but you require this format for fabrication. Simply use overlapping drill hits in the PCB tool to represent slots, then run slotifier on the drill file before sending to the fab.

The types of slots that can be produced with this tool are limited: they must be straight lines and must have the same thickness throughout. Slotifier uses a simple heuristic to convert holes to slots, and might behave unexpectedly if drill hits overlap in complex ways, see below.

Obtaining slotifier

There are presently no released versions of slotifier. The development sources may be browsed online or cloned directly using git, e.g.,

git clone


Slotifier is written in C, so a working C compiler is required.

The libgerbv library is used to process the Excellon drill file format. It must be a sufficiently recent version with support for G85 slots: the first version to support such slots is gerbv 2.7.

Furthermore, to compute the overlap relation, slotifier uses the CNearTree library.

Optionally, in order to support localized program messages the GNU libintl library (included with the GNU C library) is required.

Building from the development sources may require additional build tools.

Theory of operation

Slotifier works by locating groups of drill hits which are considered mergeable. Two holes are considered to overlap if and only if the centre of either hole is positioned within the other hole, and the transitive closure of this overlap relation gives the mergeable relation. Thus, holes A and B are mergeable if there is some sequence of overlapping holes, starting from A, which leads to B.

The mergeable property is an equivalence relation on the holes, so the holes can be partitioned into equivalence classes. Every such class with more than one hole in it is then converted into a slot as follows:

In either case, it is unspecified which option is chosen when there is more than one maximum.

For best results, the designer should ensure that mergeable holes form an approximate straight line and use the same tools.


Slotifier is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License or (at your option) any later version.