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| Knowing where foliage is present and at what height it is situated for each grid cell of a [[Heat Overlay]] is important and used in the [[Shade calculation model (Heat Overlay)|Shade]] and [[Sky view factor calculation model (Heat Overlay)|Skyview]] calculation models.
| | {{: Foliage height calculation model}} |
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| The foliage height for each grid cell can be determined in a number of ways:
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| * By supplying the [[area]]s which each hold the [[Foliage height (Heat Overlay)|height of foliage]] for the whole polygon of a particular area.
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| * By supplying a [[foliage height prequel (Heat Overlay)|prequel Grid Overlay]] which holds the foliage heights as a grid.
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| * By calculating foliage based on the height of foliage [[function]]s and their [[Foliage crown factor (Heat Overlay)|foliage crown factor]].
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| The options for determining the foliage height are mutually exclusive. Only one option will determine the foliage height.
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| It depends on the available data and the use case which option you will choose as a user. When developing future scenarios in which other users can add foliage to unknown location, it is advised to use the Foliage crown factor option.
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| ==Rasterization==
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| Regardless of the source for foliage heights, as a preparatory step for the calculations the data is transformed into a rasterized form. The end-result can be accessed via the [[foliage result type (Heat Overlay)|foliage result type]]
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| ===Foliage Areas ===
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| In case you have vector data containing foliage areas with foliage heights, you can import these by following the how-to: [[How to import foliage height areas]].
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| ===Foliage Grid Overlays===
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| In case you have a Grid Overlay with Foliage height, you can create a GeoTiff Overlay and use it as a [[Prequels (Heat Overlay)|prequel Overlay]] to configure the foliage height.
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| ===Functions===
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| In the case that foliage heights are derived from [[Function]]s with a [[foliage crown factor (Heat Overlay)|foliage crown factor]], a calculation is performed for all foliage in the project. A building is deemed foliage when it meets the following criteria:
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| * The building has the [[Function Category]] NATURE.
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| * The building has its [[Function Value]] for the [[foliage crown factor (Heat Overlay)|foliage crown factor]] greater than 0.
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| * The building is not [[exclude buildings (Heat Overlay)|excluded]] from calculations.
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| The calculation of foliage heights for all grid cells is then performed as follows:
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| # For each grid cell with foliage, the foliage diameter is calculated by multiplying the height of the foliage [[building]] with the [[foliage crown factor]]. Dividing the diameter by 2 yields the radius.
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| # This radius and foliage height is stored for each grid cell.
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| # For each grid cell i, each surrounding cell j within a search range of 100 meters is checked for a foliage height.
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| # In case the foliage height > 0, and the grid cell i is within range of the foliage diameter of cell j, the calculated foliage height for cell i is based on the distance from the center of the tree and a linear declining foliage height. The linear decline is 1:1 and currently cannot be set to a different decline. See the image below.
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| # The maximum foliage height is eventually stored as the foliage height of that cell.
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| # Additionally, the [[Bowen ratio (Heat Overlay)|Bowen ratio]] is set to 0.4 and the [[Vegetation fraction (Heat Overlay)|vegetation fraction]] is set to 1.
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| [[File:Foliage_trunk.png|400px]][[File:Foliage crown factor.png|400px]][[File:Foliage top.png|400px]]
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| {{article end | | {{article end |
