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# RegionPerimeterLength

Computes the length of the input region perimeter.

### Syntax

C++
C#

void avl::RegionPerimeterLength
(
const avl::Region& inRegion,
float& outPerimeterLength
)


### Parameters

Name Type Default Description
inRegion const Region& Input region
outPerimeterLength float&

### Description

The operation computes the perimeter length of a region shape. Because regions are pixel-precise, the literal computation of the length of the region contour would lead to the overestimation of the diagonal edges. Therefore, the filter employs the following equation to approximate the result:

Where

• sides denotes the number of pixel sides adjacent to the region background
• vertices is the number of turns to right during clockwise walk along the pixel sides of the region boundary
• a, b are constants defined as follows:

To compute the actual contour of the region, one can use RegionContours filter.

### Examples

RegionPerimeterLength run on the sample region (circular region of radius 100) computes outPerimeterLength = 627.382, while the actual perimeter of the perfect circle of radius 100 is 628.318 .