Using Polygon Input Regions

Cognex VisionPro

This topic contains the following sections.

Creating a Polygon Input Region
Region Modes
Complex Polygons

This topic shows you how to specify and configure polygons as input regions to vision tools. Not all vision tools support polygons as input regions, and among the tools that do support them, the level of support varies from tool to tool.

Creating a Polygon Input Region

To use a polygon input region, click on the Region Shape drop-down list and select CogPolygon. To append or insert vertices to the polygon, click on the add button in the grid control that displays the polygon vertices

Programming Tools Walkthrough Polygon Input Regions Poly Region clickadd

To adjust the location of a vertex in the polygon, click and drag it on the image display or select the vertex in the grid control and adjust its coordinates. To delete one or more vertices, select them in the grid control and click the delete button (the red "X").

Region Modes

As is the case with all region shapes, which pixels are selected for processing when you supply a polygon input region depends on both the region you specify and the CogRegionModeConstants that you specify. If you specify Pixel-Aligned Bounding Box mode, then all the pixels contained within the pixel-aligned bounding box of the polygon are selected. If you specify Pixel-Aligned Bounding Box Adjust Mask mode, then only the pixels that actually lie within the polygon are selected. The following figure illustrates the difference between these two modes:

Programming Tools Walkthrough Polygon Input Regions Poly Region regions

The following table lists the tools that support polygon input regions and which region mode each tool supports.

Table 1. Supported Region Modes

Tool	Bounding Box	Bounding Box Adjust Mask
2D Symbol	Yes	No
Blob	Yes	Yes
CNLSearch (train and search)	Yes	Yes
Histogram	Yes	Yes
Image Sharpness	Yes	No
IPOneImage tools	Yes	No
IPTwoImage tools	Yes	No
PDF 417	Yes	No
PMAlign (train and search)	Yes	Yes
Sobel	Yes	No

Complex Polygons

If any two segments of a polygon intersect, other than at a polygon vertex, the polygon is complex. The following figure shows a complex polygon:

Programming Tools Walkthrough Polygon Input Regions Poly Region complex

The definition of what is 'inside' and what is 'outside' of a complex polygon depends on the CogPolygonFillConstants.

The CogPolygon object lets you specify the polygon fill method programmatically using the FillMode property. If you are using a polygon input region through a tool edit control, the control does not let you select the fill method. When used through a control, the even/odd method (CogPolygonFillConstants) is always used.

Note: You can programmatically change the fill mode of a polygon region used by a tool edit control.