Improved efficiency wrf_remove_urban

README.md

@@ -55,6 +55,7 @@ Important notes
 * At the end of running `W2W`, a note is displayed that indicates the `nbui_max` value, e.g. for the sample data: `Set nbui_max to 5 during compilation, in order to optimize memory storage`. This is especially relevant for users that work with the BEP or BEP+BEM urban parameterization schemes (`sf_urban_physics = 2 or 3`, respectively). See also `num_urban_nbui` in [WRF's README.namelist](https://github.com/wrf-model/WRF/blob/master/run/README.namelist) for more info.
 * Make sure to set `use_wudapt_lcz=1` (default is 0) and `num_land_cat=41` (default is 21) in WRF's `namelist.input` when using the LCZ-based urban canopy parameters.
 * The outputs of this tool have only been tested with the most recent [WRF version 4.3.x](https://github.com/wrf-model/WRF/releases/tag/v4.3). So we advise you to work with this version as well, which is now able to ingest the urban LCZ classes by default.
+* It is possible to specify the number of nearest pixels (NPIX_NLC) to determine the dominant natural landuse in the surroundings of each urban pixel. The most frequent landuse among those pixels is used to replace the urban pixels. The distance used to find the nearest pixels is based on the great circle arc length, specifically the chord length formula (https://en.wikipedia.org/wiki/Great-circle_distance). For perfomance reasons, the nearest pixels are searched for using a k-d tree algorithm, instead of brute force over all possible pixels. Because only land natural pixels are considered to calculate the most frequent land use, we need to filter out water and other urban pixels. Thus, we need to specify the initial number of pixels that the k-d tree algorithm will select, which will be larger than NPIX_NLC. By default, NPIX_NLC**2 pixels will be selected and the nearest pixels that are not water or urban will be drawn from that initial selection. Because it is actually an area around the urban pixel, it is referred to as NPIX_AREA. 
 
 
 Arguments
@@ -67,6 +68,7 @@ Arguments
 -l --lcz-band = Band to use from LCZ file (DEFAULT: 0). For maps produced with LCZ Generator, use 1
 -f --frc-threshold = FRC_URB2D treshold value to assign pixel as urban (DEFAULT: 0.2)
 -n --npix-nlc = Number of pixels to use for sampling neighbouring natural land cover (DEFAULT: 45)
+-a --npix_area = Area in number of pixels to look for the NPIX_NLC nearest number of pixels for sampling neighbouring natural land cover (DEFAULT: NPIX_NLC**2)
 --lcz-ucp = Specify a custom lookup table for the LCZ-based Urban Canopy Parameters
 ```