Updating Third Party Projects

When updating a third party project, any changes to the imported project itself (e.g., the ThirdParty/VNL directory for VNL), should go through the UpdateThirdPartyFromUpstream.sh framework. This framework ensures that all patches to the third party projects are tracked externally and available for (preferably) upstream or other projects also embedding the library.

Any updates to projects not listed there should first convert over to this framework.

Updating a Project

Once converted, a project should be updated by applying patches to the repository specified in its UpdateFromUpstream.sh script. Once the upstream changes are merged, pulling the changes involves running the UpdateFromUpstream.sh script. This will update the local copy of the project to the version specified in UpdateFromUpstream.sh (usually a for/foo branch, like for/itk for example, but may be master or any other Git reference) and merge it into the main tree.

This requires a Git 2.5 or higher due the worktree tool being used to simplify the availability of the commits to the main checkout.

Here’s an example of updating the DoubleConversion project from tag 1.1.6 to 3.0.0, starting with updating the third-party repo

cd ./Modules/ThirdParty/DoubleConversion
git checkout for/itk
git fetch origin
git rebase --onto doubleconversion-1.1.6 doubleconversion-3.0.0
git push

Now import into ITK

cd ./Modules/ThirdParty/twisted
git checkout -b update_doubleconversion

Now you can review the change and make a merge request from the branch as normal.

Porting a Project

When converting a project, if there are any local patches, a project should be created on GitHub to track it. If the upstream project does not use Git, it should be imported into Git (there may be existing conversions available on GitHub already). The project’s description should indicate where the source repository lives.

Once a mirror of the project is created, a branch named for/foo should be created where patches for the foo project will be applied (i.e., for/itk for ITK’s patches to the project). Usually, changes to the build system, the source code for mangling, the addition of .gitattributes files, and other changes belong here. Functional changes should be submitted upstream (but may still be tracked so that they may be used).

The basic steps to import a project foo based on the tag foo-3.0.0 looks like this:

git clone https://github.com/InsightSoftwareConsortium/foo.git
cd foo/
git remote add insight git@github.com:InsightSoftwareConsortium/ITK.git:Modules/ThirdParty/foo.git
git push -u insight
git push -u insight --tags
git checkout foo-3.0.0
git checkout -b for/itk
git push --set-upstream insight for/itk

Making the initial import involves filling out the project’s UpdateFromUpstream.sh script in its directory. The UpdateThirdPartyFromUpstream.sh script describes what is necessary, but in a nutshell, it is basically metadata such as the name of the project and where it goes in the importing project.

Use the instructions in the comments at the top of the [UpdateThirdPartyFromUpstream] script to know the essential parts each third party module’s UpdateFromUpstream.sh script should have.

Make sure UpdateFromUpstream.sh is executable before commit. On Unix, run:

chmod u+x UpdateFromUpstream.sh && git add -u UpdateFromUpstream.sh

On Windows, run:

git update-index --chmod=+x UpdateFromUpstream.sh

Also add an entry to CMakeLists.txt and itk-module.cmake as appropriate.


The basic process involves a second branch where the third party project’s changes are tracked. This branch has a commit for each time it has been updated and is stripped to only contain the relevant parts (no unit tests, documentation, etc.). This branch is then merged into the main branch as a subdirectory using the subtree merge strategy.

Initial conversions will require a manual push by the maintainers since the conversion involves a root commit which is not allowed under normal circumstances. Please send an email to the mailing list asking for assistance if necessary.