QGIS TIN Polygons Assign Elevations

Introduction

This tool acts as an alternative method to using the native "MERGE" functionality in TUFLOW for 2d_zsh polygons by explicitly assigning elevation points (in a 2d_zsh template) along the polygon perimeter.
It is recommended to use this tool for Quadtree models, rather than the "MERGE" functionality, where the 2d_zsh input crosses Quadtree nesting levels.

Usage

This tool, TIN Polygons - Assign Elevations, can be found in the QGIS processing toolbox panel under TUFLOW. To open the Processing Toolbox panel, navigate to 'Processing' in the menubar and select 'Toolbox'.

Parameters

1. Polygon Layer: The polygon layer that will have elevation points created for it.
2. Selected features only: If channel(s) in the conduits layer have been selected using the 'Select Features' tool, this option will become available. If checked on, the tool will only create 1D/2D connections for the selected channel(s).
3. Raster Layer: The raster (DEM) layer that will be used to determine the elevations of the output points.
4. Vertex Distribution Option: Determines how the vertices will be distributed along the polygon perimeter.
   • Densify: Additional vertices will be inserted along the perimeter of the polygon layer at regular intervals (defined by "Vertex Interval"). This option is recommended unless the polygon layer has a negative 'Shape_Width' value, and a sufficient number of vertices.
   • Use Existing: Elevations will be assigned to the existing vertices of the polygon layer. This option should only be used if the polygon layer has a negative 'Shape_Width' value, and a sufficient number of vertices.
5. Vertex Interval (only used for Densify): The length of the interval between the vertices to be created (in map units). This value should be set to the smaller of the following:
   • Half the model cell size
   • The finest Quadtree level
6. Output Points Layer: Determines the location and filename of the output points layer. It is recommended to name the output layer with the prefix 2d_zsh.
7. Output Polygon Layer: Determines the location and filename of the output polygon layer. This layer will have the output points snapped to the polygon vertices. It is recommended to name the output layer with the prefix 2d_zsh.

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