Image Morphometric Calculator (Point)

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Image Morphometric Parameters (Point)

The Image Morphometric Parameters (Point) plugin calculates various morphometric parameters based on digital surface models. These morphometric parameters are:

  • Mean building height (zH). The average building heights from ground in meters.
  • Standard deviation of building heights (z).
  • Maximum building heights (zHmax).
  • Plan area index (λP). Fraction of buildings related to total ground area.
  • Frontal area index (λF). Fraction of building walls in wind direction related to total ground area.
  • Roughness length (z0). A parameter of some vertical wind profile equations that model the horizontal mean wind speed near the ground; in the log wind profile, it is equivalent to the height at which the wind speed theoretically becomes zero.
  • Zero displacement height (zd). The height in meters above the ground at which zero wind speed is achieved as a result of flow obstacles such as trees or buildings.

The morphometric parameters above are used to describe the roughness of a surface and are included in various local and mesoscale climate models. The parameters above will vary depending on what angle (wind direction) you are interested in. Thus, this plugin is able to derive the parameters for different directions. Preferable, a ground and 3D object DSM and a DEM should be used as input data. The 3D objects are usually buildings but can also be 3D vegetation (i.e. trees and bushes). A 3D object DSM with no ground heights makes it also possible to derive the parameters.

Location

The Image Morphometric Parameters (Point) is located at

  • UMEP
    • Pre-Processor
      • Urban Morphology
        • Image Morphometric Parameters (Point)

Running the Plugin

When you run plugin, you will see the dialog shown below. It consists of four sections. The top section let you select a point on the map canvas by either clicking at a location or by selecting a ´n existing point from a point vector layer. The next section set the parameters for the area of interest where the morphometric parameters are calculated. You also set the search interval in degrees. The next section helps you to specify the input data regarding buildings and ground. The bottom section is for specifying output and for running the calculations.

Start Dialog for the Morphometric Calculator (Point) package

Select Point on Canvas

Click on this button to create a point from where the calculations will take place. When you click button, the plugin will be disabled until you have clicked the map canvas.

Use Existing Single Point Vector Layer

Tick this in is you want to use a point from a vector layer that already exist and are loaded to the QGIS-project. The Vector point layer dropdown list will be enabled and include all point vector layer available.

Generate Study Area

This button is connected to the Search distance (m) and when you click the button a circular polygon layer (Study area) is generated. This is the area that will be used to obtain the morphometric parameters.

Wind Direction Search Interval (Degrees)

This decides the interval in search directions for which the morphometric parameters will be calculated.

Raster DSM (only Building or Vegetation) Exist

Tick this in if a 3D-object DSM without ground heights is available. 3D objects (e.g. buildings should be meters over ground.

Raster DSM (3D Object and Ground)

A raster DSM (e.g. geoTIFF) consisting of ground and e.g. building height (meters above sea level).

Raster DEM (only Ground)

A DEM (e.g. geoTIFF) consisting of pixels with ground heights (meters above sea level).

Raster DSM (only 3D Objects)

A DSM (e.g. geoTIFF) consisting of pixels with object (e.g. buildings or vegetation) heights above ground. Pixels where no objects are present should be set to zero.

Roughness Calculation Method

Here, options to choose methods for roughness calculations regarding zero displacement height (zd) and roughness length (z0) are available. For more information, see the online UMEP manual.

File Prefix

A prefix that will be included in the beginning of the output files.

Output Folder

A specified folder where result will be saved.

Run

This starts the calculations.

Close

This button closes the plugin.

Output

Two different files are saved after a successful run. The first one includes anisotropic result where the morphometric parameter for each wind direction as specified are included. The second one includes isotropic results where all directions are integrated into one value for each parameter.

Remarks

  • All DSMs need to have the same extent and pixel size.