Convert wind components from model axes to geographic E/N axes.

Convert model wind from projection to Lat/Lon axes (or back) using the map factor. This is mainly important for calculating the wind direction. Only Lambert, Rotated LatLon, rotated Mercator and Polar Stereogrphic projections are supported.

Usage

geowind(u, v, inv=FALSE, init=NULL)
geowind.init(domain)

Arguments

u, v

u and v components of the model wind. These must be geofield objects or vectors of identical length.

inv

if inv=TRUE, the vector is rotated from N/E back to the grid axes.

init

Either NULL or a list with components mapfactor and angle (e.g. the output from geowind.init). If u, v are not geofields, init can not be NULL (because angle can no longer be calculated). Both components must be the same dimension as u, v. If init=NULL, the local rotation angle and map factor are calculated prior to calculating the rotated wind vectors.

domain

A geofield or geodomain object.

Value

A list with components U,V that have the same type as the input. The wind vector has been rotated to the geographical N/E axes, or inverse. geowind.init returns a list with components angle,mapfactor that can serve as init value for later calls to geowind.

Details

geowind.init() is merely meant as a means to save computation time if the same correction must be done many times.

See also

wind.dirspeed