ITK/Release 4/Testing Data

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The Challenge

  • Data used for testing can be large.
    • ITK has three types of Data (Input, Baselines and "Large Data"). At this point, neither Baselines or Input are very large (subjective remark). "Large Data" would benefit from the MIDAS solution.
  • Data should not be stored along with the source code
    • Lorensen comment: This is an opinion, not a fact.
  • Data files change along with the evolution of the code
    • So we have to track their specific versions.
  • Adding new files should be quick and easy, ideally with a single command line
    • This was possible with ITK 3.x.
  • There must be a way to pull down the testing data corpus as a whole. You must be able to run CTest without an Internet connection.

MIDAS Proposal

  • Store ITK Testing Data in MIDAS
    • Lorensen Proposal: Keep Input and Baseline data in the ITK repository. Store Large data in MIDAS.
  • Download it at run time during ITK testing.

Data on MIDAS



The related CMake files can be found in the directory


The file


contains CMake functions that will download specific files and put them in a given directory.

The file


Contains the default file URL's.

An itk_add_test function to automatically resolve DATA{} lines is found in ITK/CMakeLists.txt.

How to find Checksum files

  • Go to the MIDAS page of the image of your interest
  • Click on the check-box "Advanced View" at the top of the page.
    • The checksums of individual files will be displayed under the filenames
    • A "Download MD5 Key File" link will be shown in front of the checksum number
  • Click on the "Download MD5 Key File" and save the file in the directory
    • ITK/Testing/MIDAS_Keys

How to locally cache testing data

It is easiest to first download all data by running an ITK build with BUILD_TESTING ON. This will download the required data into


Copy the testing data into the desired location, e.g.

 cp -r <build_dir>/ExternalData/Objects/MD5 /var/bigharddrive/


 rsync -av <build_dir>/ExternalData/Objects/MD5 /var/bigharddrive/

In new builds, point the build to the local cache by setting the CMake cache variable ExternalData_URL_TEMPLATES. The setting in this case would be


All testing data that can be found in the local cache will be used first, and the search will fall back on the default URL's if a file cannot be found.