ppi
)R/composite_ppi.R
composite_ppi.Rd
Combines multiple plan position indicators (ppi
) into a single
ppi
. Can be used to make a composite of ppi
's from multiple
radars.
composite_ppi( x, param = "DBZH", nx = 100, ny = 100, xlim, ylim, res, crs, raster = NA, method = "max", idp = 2, idw_max_distance = NA )
x | A list of |
---|---|
param | Scan parameter to composite. |
nx | number of raster pixels in the x (longitude) dimension |
ny | number of raster pixels in the y (latitude) dimension |
xlim | x (longitude) range |
ylim | y (latitude) range |
res | numeric vector of length 1 or 2 to set the resolution of the raster (see res).
If this argument is used, arguments |
crs | character or object of class CRS. PROJ.4 type description of a Coordinate Reference System (map projection). When 'NA' (default), an azimuthal equidistant projection with origin at the radar location is used. To use a WSG84 (lat,lon) projection, use crs="+proj=longlat +datum=WGS84" |
raster | (optional) RasterLayer with a CRS. When specified this raster topology is used for the output, and nx, ny, res arguments are ignored. |
method | string. Compositing method, one of "mean", "min", "max" or "idw" |
idp | numeric. inverse distance weighting power |
idw_max_distance | numeric. Maximum distance from the radar to consider in inverse distance weighting. Measuruments beyond this distance will have a weighting factor of zero. |
A ppi
.
This function composites multiple ppi objects into a ppi object that combines all data.
Either multiple ppi's of different scan elevation of the same radar may be combined, or ppi's of different radars can be composited.
Argument method
determines how values of different ppi's at the same
geographic location are combined.
"mean"
Compute the average value
"max"
Compute the maximum value. If ppi's are of the same radar and the same polar volume, this computes a max product, showing the maximum detected signal at that geographic location.
"min"
Compute the minimum value
"idw"
This option is useful primarily when compositing ppi's of
multiple radars. Performs an inverse distance weighting, where values are
weighted according to 1/(distance from the radar)^idp
The coordinates system of the returned ppi
is a WGS84
(lat,lon) datum.
This function is a prototype and under active development
# locate example volume file: pvolfile <- system.file("extdata", "volume.h5", package = "bioRad") # load the file: example_pvol <- read_pvolfile(pvolfile) # calculate a ppi for each elevation scan my_ppis <- lapply(example_pvol$scans, project_as_ppi) # overlay the ppi's, calculating the maximum value observed # across the available scans at each geographic location my_composite <- composite_ppi(my_ppis, method="max") if (FALSE) { # download basemap bm <- download_basemap(my_composite) # plot the calculated max product on the basemap map(my_composite, bm) }