Just letting double-conversion provide a *.cmake file is probably not sufficient, since the current version of ITK exposes the interface of double-conversion through itkNumberToString.h by including it without the leading subdirectory "double-conversion".
The issue has now been reported upstream with a possible patch to solve these problems: https://issues.itk.org/jira/browse/ITK-3396 Since this patch changes the ABI, I propose to only apply it with the next major ITK release (i.e. 4.9). The patch is also already available in the packaging svn: https://anonscm.debian.org/viewvc/debian-med/trunk/packages/insighttool kit/trunk/debian/patches/itk-4.8.2-find -doubleconversion.patch?revision=20625&view=markup Best, Gert