Foliage height calculation model (Heat Overlay): Difference between revisions

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Knowing where the foliage is present and at what height it is situated for each grid cell of a Heat Overlay is an important factor for the [[Shade]] and [[Skyview]] calculation models.
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.


The Foliage Height for each grid cell can be determined in three ways:
The foliage height for each grid cell can be determined in a number of ways:
* By supplying the [[Area|areas]] which each hold the height of foliage for the whole polygon of a particular area.
* By supplying the [[area]]s which each hold the [[Foliage height (Heat Overlay)|height of foliage]] for the whole polygon of a particular area.
* By supplying a geotiff which holds the foliage heights as a grid.
* By supplying a [[foliage height prequel (Heat Overlay)|prequel Grid Overlay]] which holds the foliage heights as a grid.
* By using the foliage functions and their height and [[Foliage_crown_factor|foliage crown factor]] function value.
* By calculating foliage based on the height of foliage [[function]]s and their [[Foliage crown factor (Heat Overlay)|foliage crown factor]].


The mentioned options are currently exclusive; Only one option will determine the foliage height and they currently cannot be combined.  
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 scenario's in which other users can add foliage to unknown location, it is advised to use the Foliage crown factor option.
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==
==Rasterization==
The foliage height is rasterized using the grid rasterization algorithm when the foliage height is obtained from [[Area|areas]] or [[Geotiff|geotiffs]].
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]]
In case the foliage height is determined using the foliage crown factor, it works as followed:
 
# For each grid cell, the foliage diameter is calculated by multiplying the foliage height with the foliage crown factor.
===Foliage Areas ===
# This diameter and foliage height is stored for each grid cell.
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]].
 
===Foliage Grid Overlays===
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.
 
===Functions===
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:
* The building has the [[Function Category]] NATURE.
* The building has its [[Function Value]] for the [[foliage crown factor (Heat Overlay)|foliage crown factor]] greater than 0.
* The building 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 height of the foliage [[building]] with the [[foliage crown factor]]. Dividing the diameter by 2 yields the radius.
# This radius 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.
# 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.
# 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 (Heat Overlay)|Bowen ratio]] is set to 0.4 and the [[Vegetation fraction (Heat Overlay)|vegetation fraction]] is set to 1.
[[File:Foliage_trunk.png|400px]][[File:Foliage crown factor.png|400px]][[File:Foliage top.png|400px]]
{{article end
|notes=
* The decline of the foliage height cannot be changed, it will always be linear.
* As noted above, the [[Vegetation_fraction_(Heat_Overlay)|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.


[[File:Foliage_crown_factor.png|400px]]
|howtos=
* [[How_to_adjust_the_foliage_height_and_crown_factor|How to adjust the foliage height and crown factor]]
* [[Trees and foliage tutorial]]
|seealso=
* [[Foliage_result_type_(Heat_Overlay)|Foliage (result type)]]
}}
<!--* [[FAQ_Foliage_Heat_(Overlay)|Foliage FAQ]]-->


==Notes==
{{Template:HeatOverlay_formula_nav}}
* Since the decline of the foliage height cannot be changed, it will always be linear. There are options to expand and improve this in the future.

Latest revision as of 13:16, 30 October 2023

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:

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 transformed into a rasterized form. The end-result can be accessed via the foliage result type

Foliage Areas

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.

Foliage Grid Overlays

In case you have a Grid Overlay with Foliage height, you can create a GeoTiff Overlay and use it as a prequel Overlay to configure the foliage height.

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 building is deemed foliage when it meets the following criteria:

The calculation of foliage heights for all grid cells is then performed as follows:

  1. 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.
  2. This radius and foliage height is stored for each grid cell.
  3. For each grid cell i, each surrounding cell j within a search range of 100 meters is checked for a foliage height.
  4. 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.
  5. The maximum foliage height is eventually stored as the foliage height of that cell.
  6. Additionally, the Bowen ratio is set to 0.4 and the vegetation fraction is set to 1.

Foliage trunk.pngFoliage crown factor.pngFoliage top.png

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's

See also