itkEllipsoidInteriorExteriorSpatialFunctionExample.cxx
|
Robert J. Tamburo August 17, 2001 University of Pittsburgh 749 Benedum Hall Pittsburgh, PA 15261 |
Summary
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This
example demonstrates how to create a geometrical shape within an itkImage using
Spatial Functions. Specifically, this example will use
itkEllipsoidInteriorExteriorSpatialFunction to create an itkImage consisting of
an ellipsoid.
Description
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First,
an itkImage (dimension of 3, size of 50x50x50, spacing of (1,1,1), and
origin (0,0,0)) is created and completely filled with pixels of intensity value
128. Then, itkFloodFilledSpatialFunctionConditionalIterator is used to
iterate through the image and set pixels to 256 if itkEllipsoidInteriorExteriorSpatialFunction
returns 1, meaning that it is within the interior of the ellipsoid. The
ellipsoid is defined by its axes lengths (from edge-to-edge of the ellipsoid)
as well as the orientations of these axes. This example is restricted to 3D to
allow for the visualization of the resulting image, which is done via a VTK
image file. The volume of the ellipsoid is measured by counting the number of
interior pixels of the ellipsoid. This measure can be used to verify the
resulting ellipsoid by comparing it against the calculated volume (percent
difference) of the ellipsoid given by:
, where a, b, and c are the lengths of the ellipsoid axes.
The
ellipsoid is also validated by checking that the center of the ellipsoid has
been labeled as an interior pixel (a function value of 1) by evaluating the
spatial function at the origin of the ellipsoid.
NOTE:
Orientation vectors must be orthogonal to each other and normalized!
To Use This Example
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Build and run
itkEllipsoidInteriorExteriorSpatialFunctionExample.cxx from the workspace
generated from CMake. The resulting VTK image file is stored as:
"Insight\Examples\EllipsoidInteriorExteriorSpatialFunction\ellipsoid.vtk"
Default
settings should result in an image of an ellipsoid with its axis of length 40
oriented along the (0,1,0) direction, axis of length 30 oriented along the
(1,0,0) direction, and axis of length 20 oriented along the (0,0,1) direction.
The origin of the ellipsoid is sampled and evaluated by the spatial function
and returns function value, which is 1 since the origin of the ellipsoid
is within the ellipsoid.
Results of the example (with defaults):
calculated ellipsoid volume |
12566.4 pixels |
measured ellipsoid volume |
12428 pixels |
volume error |
1.10907% |
function value |
1 |
Fig. 1: Resulting
Image Containing an Ellipsoid From This Example*
*See
"Insight\Examples\EllipsoidInteriorExteriorSpatialFunction\ellipsoid.jpg"
for snapshot of resulting image.
Insight Classes Used
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These are the Insight classes used for this example with a brief description. They appear in order of first use:
·
itkImage.h: generates
a physical image.
·
itkImageRegionIterator.h:
iterates through the pixels in the physical image and sets them to 128.
·
itkEllipsoidInteriorExteriorSpatialFunction.h:
evaluates pixels in the image and determines whether they are within the
ellipsoid or not.
·
itkFloodFilledSpatialFunctionConditionalIterator.h:
iterates the image and sets them to 256 if they are within the ellipsoid.
Possible Uses Of Ellipsoids
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The
ellipsoid images created by EllipsoidInteriorExteriorSpatialFunction are useful
for testing imaging algorithms, pixel-sampling routines, establishing geometric
domains of influence, etc.
Non-ITK Requirements
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A VTK image viewer is
needed to visualize the output file ellipsoid.vtk.
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