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Prerequisites

  • A shape file of the 'sub-areas' of the hotspot. Ideally sub-areas are created such that hazards within are similar. It is not necessary (or very desirable) to divide the hotspot such that each area contains (almost) only one receptor type.
  • A shape file of the units of the receptor of interest. A unit could be a house, but also a road section. Note: units cannot be split across areas, but must be uniquely assigned to a single area.
  • A hazard.nc file (can be a dummy simulation, as long as it contains the proper grid information)

All three files need to use the same coordinate system.

Creating a FEWS_grid.txt

Before importing the grid to QGIS, a unique gridID needs to be associated to every single grid point. It is important to do that beforehand, because the ordering of grid points may change while importing. To do so the first section (%% Add a unique gridID to your FEWS grid and save as csv file to be processed in QGIS) of this matlab script can be used: code_for_receptor_txt_files.m

Step-by-step tutorial for QGIS: Creating the <receptor>.txt in QGIS 

  1. Open a new project in QGIS

  2. Add the FEWSGrid.txt as an delimited text layer to a empty project (Layer -> Add Layer -> Add Delimited Text Layer). In the popup window select 'First record has field names', e.g.:

  3. Add the shape files (Layer -> Add Layer -> Add Vector Layer). After this the screen should look like this: 

  4. Introduce unique IDs for each sub-area (or "sector") and each receptor
    1. Select a layer and open its attribute table (Right click -> Open attribute table)
    2. 'Toggle editing mode' (pencil icon)
    3. 'Open field calculator'
      1. Check the 'Create a new field' box and choose an 'output field name' (receptorID or areaID depending on the layer you selected)
      2. Set 'Expression' to $rownum
      3. Click 'Ok'
    4. 'Save edits' and once more 'Toggle editing mode'
    5. Repeat a-d for the other layer
  5. Intersect the receptor layer with the area layer (Vector -> Geoprocessing Tools -> Intersect) and save the new layer under a new name (in this example ResBuildings_hotspot.shp)
    The resulting layer will contain all the buildings within the hotspot and associate them with the areaID of the area there in. 
  6.  Create a new polygon shape file from the FEWSGrid layer (Vector -> Geometry tools -> Voronoi Polygons) and save under a new name (in this example FEWSGrid_polygon.shp). 
  7. Intersect this FEWSGrid_polygon layer with the ResBuildings_hotspot layer. (Vector -> Geoprocessing Tools -> Intersect) and save under new name (e.g. ResBuilding_for_BN). Each polygon in the resulting shape layer is associated with a unique combination of gridID, areaID and receptorID. This information is used by the BN Adaptor to understand in which area a receptor is located and which model grid points should be used to calculated its hazard from the hazard.nc. The resulting layer should look similar to this:
  8. Save the columns areaID, receptorID and gridID (in this order!!) to a <receptor>.txt file and verify that the values in receptorID are in ascending order. 
    1. Right click on ResBuilding_for_BN -> Open Attribute Table
    2. 'Toggle editing mode'
    3. 'Delete column': all except areaID, receptorID and gridID
    4. 'Save edits', again 'Toggle editing mode' and close attribute table 
    5. Save layer as Comma Separated File (Right click on ResBuilding_for_BN -> Save As e.g. 'ResBuildings.csv')
    6. Open in excel and, if necessary, reorder the columns so that areaID is first, receptorID is second and gridID is third.
  9. Run the last two sections of above matlab code to test your csv file and to save it as txt file.


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