> For the complete documentation index, see [llms.txt](https://docs.augelab.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.augelab.com/function-blocks/blocks-reference/detections-shapes/roi-processing/check-area-polygon.md). # Check Area (Polygon) This function block lets you draw a polygon directly on an image and check whether given position coordinates fall inside that polygon. Use it to highlight a region of interest (ROI), count or mark objects inside the area, and export the polygon as a shape for downstream processing. ## đŸ“Ĩ Inputs (sockets) `Input Image (Binary Image)` This is the image on which you draw the polygon and see visual feedback. `Position Coordinate List` A list of point coordinates (x, y) to test against the drawn polygon. Multiple positions are supported. ## 📤 Outputs (sockets) `Output Image` The image with the polygon area highlighted and detected positions marked. `Polygon Coordinates` The polygon vertices as a shape that can be used by other blocks. `Object In Area` Boolean that indicates if any provided positions lie inside the polygon. `Detected Positions` The list of positions that are found to be inside the polygon. ## 🕹ī¸ Controls (widgets & interactions) `Image Canvas` Click on the image to add polygon points. The drawn polygon is displayed over the image in real time. `U` Press this key to undo the last added point. `C` Press this key to clear all polygon points and start over. `Select Area` Use the drawing interaction to create the desired polygon region. ## 🎨 Features * Visual polygon drawing over the input image with persistent preview. * Immediate visual highlighting of the selected area with a translucent overlay. * Marking of detected positions inside the polygon with clear visual markers. * Returns polygon coordinates as a reusable shape for other processing blocks. * Supports multiple input positions and reports which are inside the drawn area. ## ⚙ī¸ Running mechanism * The image provided to the `Input Image (Binary Image)` socket is displayed on the canvas. * You interactively add polygon vertices by clicking on the canvas. Each click becomes a vertex. * The drawn polygon is visually highlighted on the image. * When position coordinates are supplied to the `Position Coordinate List` socket, the block checks each point and marks those inside the polygon. * Results (highlighted image, polygon coordinates, boolean flag and detected positions) are output so other blocks can consume them. ## 📝 Usage instructions 1. Connect an image to `Input Image (Binary Image)` to enable the drawing canvas. 2. Click on the image to add polygon vertices in clockwise or counterclockwise order. 3. Use `U` to undo a point or `C` to clear and redraw the polygon. 4. Feed a list of coordinates to `Position Coordinate List` to check which points are inside the polygon. 5. Use the `Polygon Coordinates` output to pass the drawn area to other blocks for further processing. ## 💡 Tips and Tricks * To provide the points to test automatically, use `Find Object` or `Object Detection` (or `Object Detection - Custom`) upstream so detected object centers can be fed into the `Position Coordinate List` input. * Visualize results in a larger window by connecting the `Output Image` to `Show Image` for an expanded preview. * Save or log the highlighted images by connecting `Output Image` to `Image Logger` or `Image Write`. * To create multiple ROI areas, combine this block with `Image ROI Polygon Multi` to manage several polygons and pass the selected polygon coordinates further. * If you want to mark detections with rectangles instead of points, use `Draw Rectangle` or `Draw Point` downstream with the coordinates provided by this block. * For tracking workflows, feed detections from `Object Detection` into an `Object_Detection_Tracker` and use this block to check entry/exit events inside a polygonal area. ## 🛠ī¸ Troubleshooting * If clicks do not appear, ensure an image is connected to the `Input Image (Binary Image)` socket and the canvas is visible. * If points are reported outside unexpectedly, verify that coordinate format matches (x, y) and that coordinates are in the same reference frame as the displayed image. * If the polygon disappears between sessions, redraw it or store the polygon output to a persistent storage block (e.g., use outputs with file or logging blocks) and reapply when needed.