2.4. Copyright

The Ringdove convention for licenses on data, such as symbols of footprints, is to use dual licensing, plus generators and scripts may introduce a third level:

• dist license controls how the footprint may be distributed as a stand-alone footprint; for static footprint files this means distributing the footprint file (as a stand-alone footprint or as part of a footprint library)
• use license controls how the footprint can be embedded in a board file; once the footprint is placed in a board file the relevant license is the use license; this doesn't change if the whole board is exported; however if footprint is taken out from the board file and exported into a footprint file, that file is then covered by the dist license again
• if the footprint data is generated by a script or program (e.g. a parametric footprint), that script or program may have its own license, the generator license; normally the generator license controls only how the script/program can be distributed or used, but does not affect the generated footprint data

For dist license it is common to choose a permissive free software license that requires the file to remain free. This could be GPL, BSD, MIT or a suitable CC variant. In case dist license is GPL and the footprint file is to be distributed as part of a footprint library, GPL may affect the dist license on the whole library. However if the GPL'd footprint is used in a board, the board is not affected by the GPL because the use license takes precedence upon embedding.

For use license the most common choice is unlimited, which is interpreted to be equivalent to public domain or CC0. It is not practical to chose any license that requires derivative/combined works to have the same license because that'd affect the board file and could cause footprint license incompatibility.

The generator license matters much less as it generally doesn't control the use of footprint data coming from the generator. Most often generators and parametric footprints are coming with a free software license. A notable case is when a parametric footprint is ran directly from within pcb-rnd. There is a clean, well documented API between pcb-rnd and parametric footprints, which makes both ends of the equation replaceable. A parametric footprint does not rely on internals of pcb-rnd and pcb-rnd doesn't make any assumption on the internals of the parametric footprint. The parametric footprint is never linked to pcb-rnd, but is executed as a separate process. Thus the GPL license of pcb-rnd does not affect the generator and the generator license, may it be GPL, can not affect pcb-rnd or any other tool that invokes the parametric footprint in a similar manner to pcb-rnd.

Once licenses are chosen, the following metadata (see chapter 2.3) should be set:

key	importance	value (purpose of the key)
license/dist	high	name or URL of the dist license
license/use	high	name or URL of the use license
copyright	optional	free form text string containing release year, (C) and author's name; this field shall not contain any licensing information
author/contact	optional	contact information so that the author can be reached; e.g. email address

Note: license value for license/* is either the short name of a well known license in case it uniquely identifies the license (e.g. GPL2) or is an URL to the license. When distributing footprints in any form, it is best practice to include the full length license file(s) in plain text format next to the footprint file.