Great to hear that it still works!
I had to run ccmake with -DVTK_IOS_BUILD=ON
Yes, when you cross-compile you need to use a different toolchain from the get-go, so you need to let CMake know before it really configures anything/runs at all. This is true for the current custom solution in VTK, as well as the newer native CMake solution where you’d need to pass -DCMAKE_SYSTEM_NAME=iOS the first time you call CMake.
Not sure if the problem came from running cmake-gui when I first posted my question
I actually don’t know how to set variables before running CMake with cmake-gui 
.
BTW, no need to call
make install. After building the project, the vtk.framework is installed inCMAKE_FRAMEWORK_INSTALL_PREFIX.
Right, and just FYI that’s because of the custom CMake script, in VTK but you would need to if we used the iOS toolchain from CMake instead.
Have fun with it, and if you make any cool progress you can share with us please do so!