BUG: Fix MRC zero spacing for tilt series

MRC image collected as a tilt series had spacing being computed a
zero. This causes the image to be unreadable but ITK. Set the spacing
to 1 in the case.

Author: blowekamp

Modules/IO/MRC/src/itkMRCImageIO.cxx

@@ -200,20 +200,10 @@ MRCImageIO::ReadImageInformation()
     }
   }
 
-  if (header.xlen == 0.0f && header.ylen == 0.0f && header.zlen == 0.0f)
-  {
-    // if the spacing was not set in the header then this is the
-    // default
-    m_Spacing[0] = 1.0;
-    m_Spacing[1] = 1.0;
-    m_Spacing[2] = 1.0;
-  }
-  else
-  {
-    m_Spacing[0] = header.xlen / static_cast<float>(header.mx);
-    m_Spacing[1] = header.ylen / static_cast<float>(header.my);
-    m_Spacing[2] = header.zlen / static_cast<float>(header.mz);
-  }
+  // if the spacing was not set in the header then 1.0 is the default
+  m_Spacing[0] = header.xlen != 0.0f ? header.xlen / static_cast<float>(header.mx) : 1.0;
+  m_Spacing[1] = header.ylen != 0.0f ? header.ylen / static_cast<float>(header.my) : 1.0;
+  m_Spacing[2] = header.zlen != 0.0f ? header.zlen / static_cast<float>(header.mz) : 1.0;
 
   // copy the origin
   m_Origin[0] = header.xorg;

Modules/IO/MRC/test/CMakeLists.txt

@@ -34,3 +34,11 @@ itk_add_test(NAME itkMRCImageIOTest2c
         DATA{${ITK_DATA_ROOT}/Input/RGBTestImageLZW.tif}
         ${ITK_TEST_OUTPUT_DIR}/itkMRCImageIOTest2c.mrc
         38a2dcfc08812e04b1528f15ca3d2ab7)
+itk_add_test(NAME itkMRCImageIOTest2d
+        COMMAND ITKIOMRCTestDriver
+        --compare-MD5 ${ITK_TEST_OUTPUT_DIR}/itkMRCImageIOTest2d.mrc
+        96093c8573ce2b4f197f0b0bfcc574bf
+        itkMRCImageIOTest2
+        DATA{Input/tilt_uint8.mrc}
+        ${ITK_TEST_OUTPUT_DIR}/itkMRCImageIOTest2d.mrc
+        96093c8573ce2b4f197f0b0bfcc574bf)

Modules/IO/MRC/test/Input/tilt_uint8.mrc.sha512

@@ -0,0 +1 @@
+332985f125b8584b9ba158faef6294cd2f2a9e8d9fb5b7f05a74b08089b2d4e13465c1c483e42b6c4263dac9af19542a8bd5ff33dc627507ba60c976a3cb5b0a