Foliage height calculation model (Heat Overlay): Difference between revisions
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===Functions=== | ===Functions=== | ||
In the case that foliage heights are derived from [[Function]]s with a [[foliage crown factor (Heat Overlay)|foliage crown factor]], the | 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 construction is deemed foliage when it meets the following criteria: | ||
* The construction has the [[Function Category]] NATURE. | |||
* The construction has its [[Function Value]] for the [[foliage crown factor (Heat Overlay)|foliage crown factor]] is greater than 0. | |||
* The construction is not [[exclude buildings (Heat Overlay)|excluded]] from calculations. | |||
The calculation of foliage heights for all grid cells is then performed as follows: | |||
# For each grid cell with foliage, the foliage diameter is calculated by multiplying the foliage height with the [[Foliage crown factor|foliage crown factor]]. | # For each grid cell with foliage, the foliage diameter is calculated by multiplying the foliage height with the [[Foliage crown factor|foliage crown factor]]. | ||
# This diameter and foliage height is stored for each grid cell. | # This diameter and foliage height is stored for each grid cell. | ||
Revision as of 09:23, 18 December 2019
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 and Skyview calculation models.
The foliage height for each grid cell can be determined in a number of ways:
- By supplying the areas which each hold the height of foliage for the whole polygon of a particular area.
- By supplying a GeoTiff which holds the foliage heights as a grid.
- By calculating foliage based on the height of foliage functions and their foliage crown factor.
The options for determining the foliage height are mutually exclusive. Only one option will determine the foliage height.
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.
Rasterization
Regardless of the source for foliage heights, as a preparatory step for the calculations the data is rasterized.
Areas and GeoTiff
In the case of using either areas of GeoTiffs to configure the foliage height, the values from the dataset are rasterized using the grid rasterization algorithm.
Functions
In the case that foliage heights are derived from Functions with a foliage crown factor, a calculation is performed for all foliage in the project. A construction is deemed foliage when it meets the following criteria:
- The construction has the Function Category NATURE.
- The construction has its Function Value for the foliage crown factor is greater than 0.
- The construction is not excluded from calculations.
The calculation of foliage heights for all grid cells is then performed as follows:
- For each grid cell with foliage, the foliage diameter is calculated by multiplying the foliage height with the foliage crown factor.
- This diameter and foliage height is stored for each grid cell.
- For each grid cell i, each surrounding cell j within a search range of 100 meters is checked for a foliage height.
- 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.
- The maximum foliage height is eventually stored as the foliage height of that cell.
- Additionally, the Bowen ratio is set to 0.4 and the vegetation fraction is set to 1.
Notes
- The decline of the foliage height cannot be changed, it will always be linear.
- As noted above, the vegetation fraction and Bowen ratio are also changed when the foliage height is set to a positive height. This means it is also set when a geotiff or areas are used to set the foliage height.
How to
See also
