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| {| class="wikitable" | | {{db-g7}} |
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| ! [[File:Ball_ModeOff.png|200px|Ball with mode off]] !! [[File:Ball_ModeOn.png|200px|Ball with mode on]] !! [[File:Annulus_ModeOff.png|200px|Annulus with mode off]] !! [[File:Annulus_ModeOn.png|200px|Annulus with mode on]]
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| | Ball with mode off || Ball with mode on || Annulus with mode off || Annulus with mode on
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| |}
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| When using the FlatStructuringElement, the "ball" and "annulus" structuring elements have an optional flag called "foregroundHasAccurateArea". Setting this flag to true will generate structuring elements with more accurate areas, which can be especially important when morphological operations are intended to remove or retain objects of particular sizes. This mode was introduced because the original ball and annulus structuring elements have a systematic bias in the radius of +0.5 voxels in each dimension relative to the analytic definition of the radius.
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| We recommend using this mode for more accurate structuring elements. However, this mode is turned off by default for backward compatibility.
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| Here is the output of the test in the code below:
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| 2D ball of radius 5 with foregroundHasAccurateArea mode off:
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| Expected foreground area: 78.5398
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| Computed foreground area: 97
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| Foreground area error: 23.5042%
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| Writing out image Ball_ModeOff.png
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| 2D ball of radius 5 with foregroundHasAccurateArea mode on:
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| Expected foreground area: 78.5398
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| Computed foreground area: 81
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| Foreground area error: 3.1324%
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| Writing out image Ball_ModeOn.png
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| 2D annulus of radius 5 and thickness 2 with foregroundHasAccurateArea mode off:
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| Expected foreground area: 50.2655
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| Computed foreground area: 60
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| Foreground area error: 19.3662%
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| Writing out image Annulus_ModeOff.png
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| 2D annulus of radius 5 and thickness 2 with foregroundHasAccurateArea mode on:
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| Expected foreground area: 50.2655
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| Computed foreground area: 52
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| Foreground area error: 3.45071%
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| Writing out image Annulus_ModeOn.png
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| 3D ball of radius 5 with foregroundHasAccurateArea mode off:
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| Expected foreground area: 523.599
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| Computed foreground area: 739
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| Foreground area error: 41.1386%
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| 3D ball of radius 5 with foregroundHasAccurateArea mode on:
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| Expected foreground area: 523.599
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| Computed foreground area: 515
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| Foreground area error: 1.64224%
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| 3D annulus of radius 5 and thickness 2 with foregroundHasAccurateArea mode off:
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| Expected foreground area: 410.501
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| Computed foreground area: 560
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| Foreground area error: 36.4185%
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| 3D annulus of radius 5 and thickness 2 with foregroundHasAccurateArea mode on:
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| Expected foreground area: 410.501
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| Computed foreground area: 392
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| Foreground area error: 4.50703%
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| 4D ball of radius 5 with foregroundHasAccurateArea mode off:
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| Expected foreground area: 3084.25
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| Computed foreground area: 4785
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| Foreground area error: 55.143%
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| 4D ball of radius 5 with foregroundHasAccurateArea mode on:
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| Expected foreground area: 3084.25
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| Computed foreground area: 2929
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| Foreground area error: 5.03368%
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| 4D annulus of radius 5 and thickness 2 with foregroundHasAccurateArea mode off:
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| Expected foreground area: 2684.53
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| Computed foreground area: 4024
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| Foreground area error: 49.8957%
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| 4D annulus of radius 5 and thickness 2 with foregroundHasAccurateArea mode on:
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| Expected foreground area: 2684.53
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| Computed foreground area: 2504
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| Foreground area error: 6.72491%
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| ==ForegroundHasAccurateArea.cxx==
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| <source lang="cpp">
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| #include "itkFlatStructuringElement.h"
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| // Helper function
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| template< class SEType>
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| bool ComputeAreaError(SEType k, unsigned int thickness = 0);
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| int main(int, char *[])
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| {
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| int scalarRadius = 5;
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| int scalarThickness = 2;
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| bool foregroundHasAccurateArea = true;
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| typedef itk::FlatStructuringElement< 2 > SE2Type;
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| SE2Type::RadiusType r2;
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| r2.Fill( scalarRadius );
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| SE2Type k2;
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| std::cout << "2D ball of radius " << scalarRadius
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| << " with foregroundHasAccurateArea mode off:" << std::endl;
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| k2 = SE2Type::Ball( r2 );
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| ComputeAreaError(k2);
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| // Test the foregroundHasAccurateArea mode.
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| std::cout << "2D ball of radius " << scalarRadius
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| << " with foregroundHasAccurateArea mode on:" << std::endl;
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| k2 = SE2Type::Ball(r2, foregroundHasAccurateArea);
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| ComputeAreaError(k2);
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| std::cout << "2D annulus of radius " << scalarRadius
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| << " and thickness " << scalarThickness
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| << " with foregroundHasAccurateArea mode off:" << std::endl;
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| k2 = SE2Type::Annulus(r2,scalarThickness,false);
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| ComputeAreaError(k2,scalarThickness);
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| // Test the foregroundHasAccurateArea mode.
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| std::cout << "2D annulus of radius " << scalarRadius
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| << " and thickness " << scalarThickness
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| << " with foregroundHasAccurateArea mode on:" << std::endl;
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| k2 = SE2Type::Annulus(r2,scalarThickness,false,foregroundHasAccurateArea);
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| ComputeAreaError(k2,scalarThickness);
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| typedef itk::FlatStructuringElement< 3 > SE3Type;
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| SE3Type::RadiusType r3;
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| r3.Fill( scalarRadius );
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| SE3Type k3;
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| std::cout << "3D ball of radius " << scalarRadius
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| << " with foregroundHasAccurateArea mode off:" << std::endl;
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| k3 = SE3Type::Ball( r3 );
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| ComputeAreaError(k3);
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| // Test the foregroundHasAccurateArea mode.
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| std::cout << "3D ball of radius " << scalarRadius
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| << " with foregroundHasAccurateArea mode on:" << std::endl;
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| k3 = SE3Type::Ball(r3, foregroundHasAccurateArea);
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| ComputeAreaError(k3);
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| std::cout << "3D annulus of radius " << scalarRadius
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| << " and thickness " << scalarThickness
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| << " with foregroundHasAccurateArea mode off:" << std::endl;
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| k3 = SE3Type::Annulus(r3,scalarThickness,false);
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| ComputeAreaError(k3,scalarThickness);
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| // Test the foregroundHasAccurateArea mode.
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| std::cout << "3D annulus of radius " << scalarRadius
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| << " and thickness " << scalarThickness
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| << " with foregroundHasAccurateArea mode on:" << std::endl;
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| k3 = SE3Type::Annulus(r3,scalarThickness,false,foregroundHasAccurateArea);
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| ComputeAreaError(k3,scalarThickness);
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| typedef itk::FlatStructuringElement< 4 > SE4Type;
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| SE4Type::RadiusType r4;
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| r4.Fill( scalarRadius );
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| SE4Type k4;
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| std::cout << "4D ball of radius " << scalarRadius
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| << " with foregroundHasAccurateArea mode off:" << std::endl;
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| k4 = SE4Type::Ball( r4 );
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| ComputeAreaError(k4);
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| // Test the foregroundHasAccurateArea mode.
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| std::cout << "4D ball of radius " << scalarRadius
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| << " with foregroundHasAccurateArea mode on:" << std::endl;
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| k4 = SE4Type::Ball(r4, foregroundHasAccurateArea);
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| ComputeAreaError(k4);
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| std::cout << "4D annulus of radius " << scalarRadius
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| << " and thickness " << scalarThickness
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| << " with foregroundHasAccurateArea mode off:" << std::endl;
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| k4 = SE4Type::Annulus(r4,scalarThickness,false);
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| ComputeAreaError(k4,scalarThickness);
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| // Test the foregroundHasAccurateArea mode.
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| std::cout << "4D annulus of radius " << scalarRadius
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| << " and thickness " << scalarThickness
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| << " with foregroundHasAccurateArea mode on:" << std::endl;
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| k4 = SE4Type::Annulus(r4,scalarThickness,false,foregroundHasAccurateArea);
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| ComputeAreaError(k4,scalarThickness);
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| return EXIT_SUCCESS;
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| }
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| template< class SEType >
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| bool ComputeAreaError(SEType k, unsigned int thickness)
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| {
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| float expectedOuterForegroundArea = 1;
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| float expectedInnerForegroundArea;
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| if( thickness == 0 )
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| {
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| // Circle/Ellipse has no inner area to subract.
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| expectedInnerForegroundArea = 0;
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| }
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| else
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| {
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| // Annulus does have inner area to subract.
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| expectedInnerForegroundArea = 1;
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| }
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| if( SEType::NeighborhoodDimension == 2)
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| {
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| expectedOuterForegroundArea *= vnl_math::pi;
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| expectedInnerForegroundArea *= vnl_math::pi;
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| }
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| else if( SEType::NeighborhoodDimension == 3 )
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| {
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| expectedOuterForegroundArea *= 4.0/3.0 * vnl_math::pi;
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| expectedInnerForegroundArea *= 4.0/3.0 * vnl_math::pi;
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| }
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| else if ( SEType::NeighborhoodDimension == 4 )
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| {
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| expectedOuterForegroundArea *= 0.5 * vnl_math::pi * vnl_math::pi;
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| expectedInnerForegroundArea *= 0.5 * vnl_math::pi * vnl_math::pi;
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| }
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| else
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| {
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| return EXIT_FAILURE;
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| }
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| for( unsigned int i = 0; i < SEType::NeighborhoodDimension; i++ )
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| {
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| expectedOuterForegroundArea *= k.GetRadius()[i];
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| expectedInnerForegroundArea *= (k.GetRadius()[i] - thickness);
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| }
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| float expectedForegroundArea = expectedOuterForegroundArea - expectedInnerForegroundArea;
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| // Show the neighborhood if it is 2D.
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| typename SEType::Iterator SEIt;
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| if( SEType::NeighborhoodDimension == 2 )
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| {
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| for( SEIt = k.Begin(); SEIt != k.End(); ++SEIt )
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| {
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| std::cout << *SEIt << "\t";
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| if( (SEIt - k.Begin()+1) % k.GetSize()[0] == 0 )
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| {
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| std::cout << std::endl;
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| }
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| }
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| }
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| // Compute the area/volume.
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| float computedForegroundArea = 0;
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| for( SEIt = k.Begin(); SEIt != k.End(); ++SEIt )
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| {
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| if( *SEIt )
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| {
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| computedForegroundArea++;
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| }
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| }
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| std::cout << "Expected foreground area: " << expectedForegroundArea << std::endl;
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| std::cout << "Computed foreground area: " << computedForegroundArea << std::endl;
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| std::cout << "Foreground area error: "
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| << 100 * vnl_math_abs(expectedForegroundArea-computedForegroundArea)/expectedForegroundArea
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| << "%" << "\n\n";
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|
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| return EXIT_FAILURE;
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| }
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| </source>
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| {{ITKCMakeLists|{{SUBPAGENAME}}}}
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