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 = "all",
nx = 100,
ny = 100,
xlim,
ylim,
res,
crs,
raster = NA,
method = "max",
idp = 2,
idw_max_distance = NA,
coverage = FALSE
)
A list of ppi
objects.
The scan parameter name(s) to composite. An atomic vector of character strings can be provided to composite multiple scan parameters at once. To composite all available scan parameters use 'all' (default).
number of raster pixels in the x (longitude) dimension
number of raster pixels in the y (latitude) dimension
x (longitude) range
y (latitude) range
numeric vector of length 1 or 2 to set the resolution of the raster (see res).
If this argument is used, arguments nx
and ny
are ignored. Unit is identical to xlim
and ylim
.
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"
(optional) RasterLayer with a CRS. When specified this raster topology is used for the output, and nx, ny, res arguments are ignored.
string. Compositing method, one of "mean", "min", "max" or "idw". Provide a list of methods names of length(param) to apply different methods to each of the parameters.
numeric. inverse distance weighting power.
numeric. Maximum distance from the radar to consider in inverse distance weighting. Measurements beyond this distance will have a weighting factor of zero.
logical. When TRUE adds an additional "coverage" parameter to the ppi
with the
number of PPIs covering a single composite ppi
pixel.
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, unless a different crs
is provided. If only
res
is provided, but no crs
is set, res
is in
meter units and the origin of the composite ppi
is set to the
mean (lat, lon) location.
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)
#> Warning: CRS object has comment, which is lost in output; in tests, see
#> https://cran.r-project.org/web/packages/sp/vignettes/CRS_warnings.html
#> Warning: CRS object has comment, which is lost in output; in tests, see
#> https://cran.r-project.org/web/packages/sp/vignettes/CRS_warnings.html
#> Warning: CRS object has comment, which is lost in output; in tests, see
#> https://cran.r-project.org/web/packages/sp/vignettes/CRS_warnings.html
# 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")
# \dontrun{
# download basemap
bm <- download_basemap(my_composite)
#> Downloading zoom = 9 ...
#> Map tiles by Stamen Design, under CC BY 3.0. Data by OpenStreetMap, under ODbL.
# plot the calculated max product on the basemap
map(my_composite, bm)
#> Warning: 'length(x) = 3 > 1' in coercion to 'logical(1)'
#> Warning: 'length(x) = 3 > 1' in coercion to 'logical(1)'
#> Warning: Discarded ellps WGS 84 in Proj4 definition: +proj=merc +a=6378137 +b=6378137 +lat_ts=0 +lon_0=0 +x_0=0 +y_0=0 +k=1 +units=m +nadgrids=@null +wktext +no_defs
#> Warning: Discarded datum WGS_1984 in Proj4 definition
#> Warning: CRS object has comment, which is lost in output; in tests, see
#> https://cran.r-project.org/web/packages/sp/vignettes/CRS_warnings.html
#> Warning: Discarded ellps WGS 84 in Proj4 definition: +proj=merc +a=6378137 +b=6378137 +lat_ts=0 +lon_0=0 +x_0=0 +y_0=0 +k=1 +units=m +nadgrids=@null +wktext +no_defs +type=crs
#> Warning: Discarded datum World Geodetic System 1984 in Proj4 definition
# }