QGIS Create a TIN: Difference between revisions
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This example uses the DEM and GIS files from <u>[[Tutorial_M02#Part_2_-_Other_Topographic_Updates|Tutorial Module 2 (part 2)]]</u>.
==Densify Merge Polygon Vertices==
Densify the merge polygon vertices using the QGIS processing tool 'Densify by Interval'. For more information about this tool, please refer to the <u>[https://docs.qgis.org/3.34/en/docs/user_manual/processing_algs/qgis/vectorgeometry.html#densify-by-interval QGIS Documentation - Densify by Interval]</u>.
<ol>
<li>In QGIS, go to Processing > Toolbox from the top dropdown menu options to open the Processing Toolbox.<br>
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<li>Go to 'Vector geometry' in the processing tool list and select 'Densify by interval'. This opens the dialog shown below:
*Input layer: Select the merge polygon (e.g. '''2d_zsh_M02_landscape_002_R''').
*Interval between vertices to add: This value should set to the smaller of the following two values - half the model cell size, or the finest quadtree level.
*Densified: Leave as default.
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[[File: QGIS_Create_TIN_Densify_Polygon_02.png]]<br>
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</ol>
==Extract Elevation of Polygon Vertices from DEM==
Extract elevation at polygon vertices from DEM using the QGIS processing tool 'Drape (set Z value from raster)'. For more information about this tool, please refer to <u>[https://docs.qgis.org/3.34/en/docs/user_manual/processing_algs/qgis/vectorgeometry.html#drape-set-z-value-from-raster QGIS Documentation - Drape]</u>.
<ol>
<li>Go to 'Vector geometry' in the processing tool list and select 'Drape (set Z value from raster)'. This opens the dialog shown below:
*Input layer: '''Densified_Polygon'''
*Raster layer: Select the DEM file.
<li>Leave all other options as default and ensure 'Open output file after running algorithm' is ticked on.
<li>Click 'Run'. Once the tool is finished, click 'Close'. <br>
<br>
[[File: QGIS_Create_TIN_Drape_Polygon_01.png]]<br>
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<li>The resulting layer, called '''Draped''' will appear in the QGIS Layers panel. Right click '''Draped''' and select 'Rename Layer'. Rename the layer to '''Draped_Polygon'''.
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==Generate IDW Interpolation==
Generate a IDW (Inverse Distance Weighted) interpolation of the z shape points layer, using the QGIS processing tool 'IDW Interpolation'. For more information about this tool, please refer to <u>[https://docs.qgis.org/3.34/en/docs/user_manual/processing_algs/qgis/interpolation.html#qgisidwinterpolation QGIS Documentation - IDW Interpolation]</u>.
<ol>
<li>Go to 'Interpolation' in the processing tool list and select 'IDW Interpolation'. This opens the dialog shown below:
*Vector layer: Select the z shape points layer (e.g. '''2d_zsh_M02_landscape_002_P''').
*Interpolation attribute: Select '''Z'''. This is the attribute that contains elevation data.
*Click [[File: QGIS_3D_Animation_add_keyframe_button_01.png|30px]] to add the vector layer to the table. Repeat the above two points for all points layers within the merge polygon extent.
*Distance coefficient P: Leave as default.
*Extent: Click [[File: interpolation_extent_icon.png|40]] and select 'Calculate from Layer' >> 'Draped_Polygon'.
*Interpolated: Leave as default.
*Tick on 'Open output file after running algorithm'.
<li>Click 'Run'. Once the tool is finished, click 'Close'. <br>
<br>
[[File: QGIS_Create_TIN_IDW_Interpolation_01.png]]<br>
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<li>The resulting file, called '''Interpolated''' will appear in the QGIS Layers panel. <br>
<br>
[[File: QGIS_Create_TIN_IDW_Interpolation_02.png]]<br>
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</ol>
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