[vtk-developers] Converting baselines from VTKData to ExternalData

[Brad King]

Hi Folks,

VTKData keeps our test data separate from the VTK source tree so
they are not versioned together.  Historically we've gotten away
with this by using checkouts with an approximately matching date.
When developers forget to update VTKData locally tests fail
mysteriously.  More recently we've had problems with testing
topics in VTK's Gerrit instance:

 Policy for changing VTKData or VTKLargeData with Gerrit topics
 http://www.vtk.org/pipermail/vtk-developers/2013-March/013329.html

 Adding VTKData and VTKLargeData as optional submodules
 http://www.vtk.org/pipermail/vtk-developers/2013-March/013196.html

In order to address this problem we will start using the CMake
ExternalData module to keep test data versioned with our source
tree without actually paying the cost of keeping them in the
repository:

 CMake ExternalData: Using Large Files with Distributed Version Control
 http://www.kitware.com/source/home/post/107

 CMake ExternalData Module Documentation
 http://www.cmake.org/cmake/help/v2.8.11/cmake.html#module:ExternalData

ITK has used this approach successfully for a couple years now.

We will start by converting the baseline data.  It will now be
referenced by Testing/Data/Baseline/*.md5 content links inside
each module directory in the source tree.  I've uploaded all
VTKData/Baseline and VTKLargeData/Baseline images to MIDAS:

 http://midas3.kitware.com/midas/community/27

with a folder structure mirroring the source tree modular layout.

I've published a topic to update the source tree here:

 https://github.com/bradking/VTK/tree/use-ExternalData

Please try it out.  **I plan to merge this to VTK master next week**.

For now I squashed it temporarily into a single commit for testing:

 http://review.source.kitware.com/#/t/2771/

I've already updated the CDash at Home clients and Kitware-maintained
nightly dashboard scripts to use a persistent local object store
and avoid downloading any data file more than once.

-Brad