RegionsOperatorsmRgnPolygonialArea Method

Parameters

regions

Type: MediaCy.IQL.FeaturesMcRegions

Return Value

Type: McMeasure

Usage Note

In Visual Basic and C#, you can call this method as an instance method on any object of type McRegions. When you use instance method syntax to call this method, omit the first parameter. For more information, see Extension Methods (Visual Basic) or Extension Methods (C# Programming Guide).

This is a boundary geometry based measurement, so it is not dependent on pixel counts and is accurate for sub-pixel locations of region boundaries. It is only valid for boundaries that do not cross themselves (i.e., no figure-8's). For regions created by the McThreshold.Execute or McFeatures.SetFromMask methods (features of Type mcftScanList), holes in the blob are not significant for this measurement. The area measured from the outline of region features of Type mcftScanList depends on how the outline is placed around the scanlist blob. When the OptionFlags mcofOutlinePixelTiles bit is set (thus forcing the outline to follow the boundary pixels as if they were square tiles), the measured mRgnPolygonialArea will equal the count of pixels, including holes, in the blob times the area of one pixel. The mRgnArea measurement is a direct count of pixels under and interior to the region boundary, excluding any holes, so in this case these measurements will be equal if there are no holes in the blob. However, if the OptionFlags mcofOutlinePixelTiles bit is clear, or if the region feature boundary is not derived from a feature of Type mcftScanList, then the mRgnArea will almost always be larger than the area reported by the mRgnPolygonialArea. This is because mRgnPolygonialArea is computed from from the boundary outline and thus excludes any portion of each border pixel "tile" that is not fully enclosed by the boundary polygon. For example for an 8 by 8 pixel rectangle of foreground pixels starting at the orign, the McRegions feature created by McRegions.Threshold.Execute with the OptionFlags mcofOutlinePixelTiles bit is clear will a box with its upper left X,Y coordinate at 0,0 while its lower right coordinate will be at 7,7. These coordinates fall on the centers of the border pixels. In this case the mRgnArea measurement reports an area of 64 square pixel units (the count of the 8 by 8 block), but the mRgnPolygonialArea reports an area of 49 square units (the area of the 7 by 7 border rectangle). With the OptionFlags mcofOutlinePixelTiles bit set, both measurements report 64. By default, the OptionFlags mcofOutlinePixelTiles bit is clear, so the outline polygon vertices are placed on the centers of border pixels, not on the "outer edge" of the border pixel, treated as a tile. The logic behind this is that pixel intensities are actually seen as an array of point values, not "tiles". And the best quess as to the location of each of these point values is in the center of the pixel "tile", not on one of the tile's borders.