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Point In Polygon Tool

Overview​

The PointInPolygonTool is a QGIS tool designed to help users create points on the boundary of a polygon layer. It allows users to:

  • Snap points to the boundary of a polygon.
  • Create a new point at a specified distance between two clicked points on the polygon boundary.
  • Visualize snapping and preview points using rubber bands.

Key Features​

  • Snapping to Polygon Boundary: Automatically snaps points to the nearest boundary of the selected polygon layer.
  • Distance-Based Point Creation: Allows users to specify a distance to create a new point between two clicked points.
  • Visual Feedback: Provides visual feedback using rubber bands for snapping, preview points, and guide lines.
  • Layer Management: Handles layer removal and ensures the tool remains functional even if layers are deleted.

How to Use the Tool​

1. Setting Up the Tool

  • Ensure you have a valid polygon layer loaded in QGIS.
  • Activate the PointInPolygonTool from the plugin menu or toolbar.

2. Selecting the Target Layer

  • Select the polygon layer or Line layer from layer panel you want to work with. The tool will automatically check if the layer is valid.

3. Snapping to the Polygon Boundary

  • Move the mouse cursor near the boundary of the polygon. The tool will snap to the nearest point on the boundary and display a red or green rubber band to indicate the snap point.

4. Creating Points

  • First Click: Click on the polygon boundary to set the first point. A dialog will appear prompting you to enter the distance (in meters) for the new point.
  • Second Click: Click on another point on the polygon boundary. The tool will create a new point at the specified distance between the two clicked points.

5. Canceling the Operation

  • Right-click to cancel the current operation. This will clear all rubber bands and reset the tool.

6. Visual Feedback

  • Red Rubber Band: Indicates the first snap point.
  • Green Rubber Band: Indicates the second snap point.
  • Blue Rubber Band: Shows the preview of the new point based on the specified distance.
  • Dashed Line: Displays the guide line between the first and second points.

Error Handling​

  • Invalid Layer: If the selected layer is invalid or deleted, the tool will display an error message and reset.
  • Invalid Distance: If the entered distance is zero or negative, the tool will prompt you to enter a valid distance.
  • Point Inside Polygon: If you click inside the polygon (not on the boundary), the tool will notify you to click on the boundary.

Tool Deactivation​

  • When deactivating the tool, it will:
    • Clear all rubber bands.
    • Reset the tool state.
    • Disconnect from layer removal signals.
    • Refresh the canvas.

Tips​

  • Ensure the polygon layer is valid and has a valid CRS.
  • Use the rubber bands as visual guides to accurately place points on the polygon boundary.
  • If the tool behaves unexpectedly, check the QGIS message bar for error messages.

Troubleshooting​

  • Tool Not Snapping: Ensure the polygon layer is valid and the snapping is enabled in QGIS settings.
  • No Points Created: Verify that the distance entered is valid and greater than zero.
  • Layer Not Found: If the point layer is missing, the tool will create a new one named "Snapped Points".