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3.19. Urban Morphology: Morphometric Calculator (Grid)

  • Contributor:

    Name

    Institution

    Christoph Kent

    Reading

    Fredrik Lindberg

    Gothenburg

    Brian Offerle

    previously Indiana University; FluxSense AB

    Sue Grimmond

    Reading

    Niklas Krave

    Gothenburg
  • Introduction

    The Morphometric Calculator (Grid) pre-processor calculates various morphometric parameters based on digital surface models.

  • Dialog box
    ../_images/Morph_Calc.jpg

    Fig. 3.37 The dialog for the Morphometric Calculator (Grid)

  • Search Throughout the Grid Extent

    Select if the search should be performed from one side of the grid to the opposite side. Select the other option (Search from Grid Centroid if the search should start from the centroid of the grid. Setting the Search distance can then allow for the search to extent beyond the grid. See the figure below for illustration. The left one performs a search using the grid extent whereas the right illustrates a search from the centroid and extending outside of the grid.

    ../_images/Grid_Extent.png

    Fig. 3.38 The two search methods for the Search Throughout the Grid Extent option

  • Wind Direction Search Interval (degrees)

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

  • Vector Polygon Grid

    Here the grid polygon layer should be specified.

  • ID Field

    Choose an attribute from the selected polygon layer that will be used to separated the different polygon objects from each other. An attribute field of unique numbers or letters should be used.

  • Add results to polygon grid

    Tick this in if you would like to save a isotropic results in the attribute table for your polygon vector grid.

  • Raster DSM (only 3D Objects) Exist

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

  • Raster DSM (3D Objects and Ground)

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

  • Raster DEM (only Ground)

    A DEM (e.g. geoTIFF) consisting of pixels with ground heights (metres 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

    Options to choose methods for roughness calculations regarding zero-plane displacement height (zd) and roughness length (z0) are available.

  • File Prefix

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

  • Ignore NoData pixels

    Tick this in if NoData pixels should be ignored and calculation of grid should be performed eventhough NoData pixels exists within that grid. Nodata pixels are set to the average pixel values of the DEM.

  • Output Folder

    A specified folder where result will be saved.

  • Run

    Starts the calculations

  • Close

    Closes the plugin

  • Output

    Two different files are saved after a successful run.

    1. Anisotropic result where the morphometric parameters for each wind direction as selected are included.

    2. Isotropic results where all directions are integrated into one value for each parameter.

  • Remarks

    1. Units of wai is non dimensional (area building walls / total horizontal area).

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

    3. Polygon grids must be squared (or rectangular) and allinged with the CRS used. This will be fixed in future versions so that any shaped grid can be used (see issue #12 in the repository).

  • References

    • Kent CW, CSB Grimmond, J Barlow, D Gatey, S Kotthaus, F Lindberg, CH Halios 2017: Evaluation of urban local-scale aerodynamic parameters: implications for the vertical profile of wind and source areas Boundary Layer Meteorology 164 183–213 doi: [10.1007/s10546-017-0248-z https://link.springer.com/article/10.1007/s10546-017-0248-z]

    • Kent CW, S Grimmond, D Gatey Aerodynamic roughness parameters in cities: inclusion of vegetation Journal of Wind Engineering & Industrial Aerodynamics http://dx.doi.org/10.1016/j.jweia.2017.07.016

    • Grimmond CSB and Oke TR (1999) Aerodynamic properties of urban areas derived from analysis of surface form. J Appl Meteorol 38: 1262-1292