The typedef `typedef itk::Matrix < double, 3, 3 > DirectionType;` is defined twice: [here](https://github.com/SlicerRt/plastimatch/blob/slicerrt-1.9.3-2022.06.15-77b40bd3/src/plastimatch/base/itk_image.h#L16) and [here](https://github.com/SlicerRt/plastimatch/blob/slicerrt-1.9.3-2022.06.15-77b40bd3/src/plastimatch/base/direction_cosines.h#L17), hence [a compilation error](https://slicer.cdash.org/viewBuildError.php?buildid=2827651). Possible fix: In file `direction_cosines.h` delete DirectionType definition and add `itk_image.h` header ``` .... #include "itk_image.h" #include "plm_math.h" #define DIRECTION_COSINES_IDENTITY_THRESH 1e-9 #define DIRECTION_COSINES_EQUALITY_THRESH 1e-9 namespace itk { template<class T, unsigned int NRows, unsigned int NColumns> class Matrix; } //typedef itk::Matrix < double, 3, 3 > DirectionType; .... ```