[Insight-users] Using ITK externally

[Neil Killeen]

G'day all

I am now attempting to include ITK (and VTK for that matter)
in an external project. I am finding this process less than clear...


1) I have installed ITK  as

  /usr/local/lib/itk
  /usr/local/include/itk

  However, I installed these files by copying them from where
  the ITK install process

% make install

  put them.  This is because it put them somewhere silly (under the
  vtk build tree in fact) because i did not get control over
  the itk install location.  I posted a message about this a few days
  ago.



2) The ITK include tree is hierarchical in /usr/local/include

  thus

% ls /usr/local/include/itk/
Algorithms      Common          Numerics        Utilities
BasicFilters    IO              SpatialObject   itkConfigure.h


  However, none of the ITK source tree code  reflects this.
  ITK .h files are just included with no directory prefix, whether
  they live in Algorithms or Utilities or wherever.

  This is handled by specifying multiple locations to find the
  include files via the cmake command

  SET(ITK_INCLUDE_DIRS ...)



3) Clearly I don't want to have to hard-code all of the include
   directories.I am tempted to just move all of the nested files into
   /usr/local/include/itk

   and that will be that.  However, I realize that there is a file,

   ITKConfig.cmake.in

   which I am supposed to include in my own CMakeLists.txt file
   to configure ITK for me.

   But I can't understand the philosophy nor make it work.  I have to do
   something like this in my CMakeLists.txt file in my own project source
   tree:

# Configure ITK
SET (ITK_DIR /nfs/source/itk)               # Tell it where to find ITK source tree
INCLUDE(${ITK_DIR}/ITKConfig.cmake.in)      # Invoke configure
INCLUDE_DIRECTORIES(${ITK_INCLUDE_DIRS})    # Set include directories


   But this does not and cannot work.   This is because it has no way of
   knowing where I have installed the ITK system.   I did that by hand
   (see 1) above).


4) I don't actually see how the statement

    INCLUDE(${ITK_DIR}/ITKConfig.cmake.in)      # Invoke ITK configure

   could ever work, becuase the install location is in the cmake Cache
   file in the binary tree, not anywhere in the source tree.

   Now I realize that when I invoke, say

   % ccmake $ITKSRC

   that this defines variables locating the directory from which
   I am running cmake (the PROJECT_BINARY_DIR variable) so that cmake
   does know the present binary tree location (so that it can output
   the binaries to the right place).

   However, I am running cmake now to build MY system, not ITK or VTK
   or whatever, so it can compute PROJECT_BINARY_DIR for my project.
   But it can't possibly compute it for when ITK was built since that
   information is not cached in the ITK source tree which it is accessing.
   So how can ITKConfig.cmake.in ever compute ITK_BINARY_DIR or
   ITK_INSTALL_DIR (if there was one) when I am building my project.

   Perhaps there is something simple I am just failing to understand.
   I hope so :-)




Questions:

1) Why are the ITK include files installed hierarchically, when they
are never invoked that way in the source code ?  I notice that
VTK include files are just dumped in one directory.  Then its
trivial to include /usr/local/include/vtk in the directory path.

ALso, the ITK libraries are not installed hieararchically, so it is
in fact easy for me to specify the linker directory as

/usr/local/lib/itk


2) How do I automatically determine the ITK include directories when
i have installed them as I did (above) ?


3) In many of the install include directories, there are files with
   .txx extensions.  What are they ?  They hold C++ code.




thanks again
Neil