[Insight-users] Creating a 2D binary image from a polygon

[AurelieC]

Hello,

I have a 2D polygonal region of interest defined by a list of points (x and
y coordinates). I am trying to create a new image of a given size which will
be white inside the polygon and black outside.

What I tried to do : 
I create a mesh, I add in the mesh the points, then LineCell between the
points and vertexCell at each points.
Then I create a MeshSpatialObject which take the created mesh.
Then I try to create a binary image using the MeshSpatialObject : first I
was using the MeshToImageFilter but it did not work so I tried to scan all
the image and for each pixel I just check if it is inside or outside the
polygon, if it is inside it gets the value 1.
The code compiles, but nothing happens, no point is considered as inside the
mesh, the outside image is black, so I think I made a mistake while creating
the mesh. Maybe I should use PolygonCell, or PolygonGroupSpatialObject?

Please help me.

This is my code:


// creating the mesh

typedef   float   PixelType;  
const unsigned int Dimension = 2;
typedef itk::Mesh< PixelType, Dimension>   MeshType;
MeshType::Pointer  mesh = MeshType::New();

// adding points and creating the cells

MeshType::PointType p;

typedef MeshType::CellType CellType;
typedef itk::LineCell< CellType > LineType;
typedef itk::VertexCell< CellType > VertexType;

// tab contained the coordinates of each points
for (int i = 0; i < nbPoint; i++)
{
    p[0] = tab[i*2];
    p[1] = tab[i*2+1];
    mesh->SetPoint(i,p);
}

//creating lines between points
CellType::CellAutoPointer cellpointer;

for(int cellId=0; cellId < nbPoint-1; cellId++)
{
    cellpointer.TakeOwnership( new LineType );
    cellpointer->SetPointId( 0, cellId ); // first point
    cellpointer->SetPointId( 1, cellId+1 ); // second point
    mesh->SetCell( cellId, cellpointer ); // insert the cell
}

cellpointer.TakeOwnership( new LineType );
cellpointer->SetPointId( 0, (nbPoint-1) ); // first point
cellpointer->SetPointId( 1, 0 ); // second point
mesh->SetCell( nbPoint-1, cellpointer); // insert the cell

for(int cellId=0; cellId < nbPoint; cellId++)
{
    cellpointer.TakeOwnership( new VertexType );
    cellpointer->SetPointId( 0, cellId );
    mesh->SetCell( cellId + nbPoint, cellpointer );
}


std::cout << "# Points= " << mesh->GetNumberOfPoints() << std::endl;
std::cout << "# Cell  = " << mesh->GetNumberOfCells() << std::endl;


// creating the MeshSpatialObject
typedef itk::MeshSpatialObject<MeshType>     MeshSpatialObjectType;
MeshSpatialObjectType::Pointer myMeshSpatialObject = 
MeshSpatialObjectType::New();

myMeshSpatialObject->SetMesh(mesh);


// creating the output image

typedef itk::Image<float, 2>      ImageType;
ImageType::Pointer image = ImageType::New();

// dimX and dimY given dimensions
size[0] = d->dimX;
size[1] = d->dimY;
ImageType::IndexType start;
start[0] = 0; // first index on X
start[1] = 0; // first index on Y
ImageType::RegionType region;
region.SetSize( size );
region.SetIndex( start );

image->SetRegions( region );
image->Allocate();

myMeshSpatialObject->Update();


// region to scan. I reduce the region to scan using the
mesh->GetBoundingBox()

typedef itk::FixedArray< float, 4> FixedArraySize;
FixedArraySize test;
myMeshSpatialObject->GetBoundingBox()->ComputeBoundingBox();
test =  myMeshSpatialObject->GetBoundingBox()->GetBounds();

ImageType::RegionType roi;

size[0] = int(test[1])+2 -  int(test[0]);
size[1] =  int(test[3]) +2 - int(test[2]);
roi.SetSize( size );
// roi.SetIndex( start );


// test each pixel of the boundingbox, check if it is inside or outside the
polygon
itk::Point<float,2> point;
typedef itk::ImageRegionIterator<ImageType> Iterator;
Iterator it( image, roi );
it.GoToBegin();
  
  while( !it.IsAtEnd() )
    {

    image->TransformIndexToPhysicalPoint(it.GetIndex(), point );
    
    if (myMeshSpatialObject->IsInside(point))
    {
	qDebug() << "isinside "<< endl; // no point is in this case...
	image->SetPixel(it.GetIndex(), 1);
    }
    else 
	image->SetPixel(it.GetIndex(), 0);

    ++it;
    }



// write the result

typedef itk::ImageFileWriter< ImageType > ImageWriterType;
ImageWriterType::Pointer imgWriter = ImageWriterType::New();
imgWriter->SetInput(image);
imgWriter->SetFileName(filename);
imgWriter->Update();




Thank you!
-- 
View this message in context: http://www.nabble.com/Creating-a-2D-binary-image-from-a-polygon-tp22804986p22804986.html
Sent from the ITK - Users mailing list archive at Nabble.com.