ENH: Can now read LineMesh's from VTK files

Source/Geometry/imstkGeometryUtilities.cpp

@@ -360,6 +360,12 @@ GeometryUtils::copyToLineMesh(vtkSmartPointer<vtkPolyData> vtkMesh)
     std::shared_ptr<VecDataArray<double, 3>> vertices = copyToVecDataArray(vtkMesh->GetPoints());
     std::shared_ptr<VecDataArray<int, 2>>    cells    = copyToVecDataArray<2>(vtkMesh->GetPolys());
 
+    // If polys is empty use lines instead
+    if (cells->size() == 0)
+    {
+        cells = copyToVecDataArray<2>(vtkMesh->GetLines());
+    }
+
     auto mesh = std::make_unique<LineMesh>();
     mesh->initialize(vertices, cells);
 

Source/MeshIO/imstkVTKMeshIO.cpp

@@ -250,7 +250,18 @@ VTKMeshIO::readVtkGenericFormatData(const std::string& filePath)
 
     if (vtkSmartPointer<vtkPolyData> vtkMesh = reader->GetPolyDataOutput())
     {
-        return GeometryUtils::copyToSurfaceMesh(vtkMesh);
+        // Try to convert to surface mesh, if no elements exist try reading as a line mesh
+        std::shared_ptr<SurfaceMesh> surfMesh = GeometryUtils::copyToSurfaceMesh(vtkMesh);
+        if (surfMesh->getNumTriangles() > 0)
+        {
+            return surfMesh;
+        }
+        std::shared_ptr<LineMesh> lineMesh = GeometryUtils::copyToLineMesh(vtkMesh);
+        if (lineMesh->getNumLines() > 0)
+        {
+            return lineMesh;
+        }
+        return GeometryUtils::copyToPointSet(vtkMesh);
     }
 
     if (vtkUnstructuredGrid* vtkMesh = reader->GetUnstructuredGridOutput())