# solarIncidenceAngle: Compute solar incidence angle In environmentalinformatics-marburg/satelliteTools: What the package does (short line)

## Description

Compute the solar incidence angle over non-planar surfaces following the equation from Duffie and Beckman (2013).

## Usage

 ``` 1 2 3 4 5 6 7 8 9 10 11 12``` ```## S4 method for signature 'POSIXt' solarIncidenceAngle(x, dem, formula = c("Cooper", "Spencer"), neighbors = 8L, unit = c("radians", "degrees")) ## S4 method for signature 'character' solarIncidenceAngle(x, dem, formula = c("Cooper", "Spencer"), neighbors = 8L, unit = c("radians", "degrees"), ...) ## S4 method for signature 'Raster' solarIncidenceAngle(x, origin = strptime("1993-01-01", "%Y-%m-%d"), dem, formula = c("Cooper", "Spencer"), neighbors = 8L, unit = c("radians", "degrees"), ...) ```

## Arguments

 `x` A date-time object of class `POSIX*`, or a `character` object that can be coerced by `strptime`, or a `Raster*` object holding such information. `dem` `RasterLayer`, digital elevation model in EPSG:4326 (see http://spatialreference.org/ref/epsg/wgs-84/). `formula` `character`, formula from which to calculate the angular declination of the sun, see `declination`. `neighbors` `integer`, number of focal cells from which to calculate surface slope and aspect, see `terrain`. `unit` `character`, determines whether to return the solar incidence angle in radians (default) or degrees. `...` If `x` is a `character` object, formatting arguments passed on to `strptime`, or if `x` is a `Raster*` object, formatting arguments related with the specified `origin`. `origin` A `POSIX*` or `character` object that defines the origin of `x`, see `solarHourAngle`.

## Value

A `Raster*` object with pixel-wise solar incidence angles.

## Note

An angle of more than 90 degrees, or likewise `pi/2`, indicates that the sun is behind the surface.

## References

Duffie JA, Beckman WA (2013) Solar Engineering of Thermal Processes. Wiley: Hoboken, New Jersey, ISBN: 978-0-470-87366-3, http://eu.wiley.com/WileyCDA/WileyTitle/productCd-0470873663.html.

`declination`, `solarHourAngle`, `terrain`.
 ```1 2 3 4 5 6 7``` ```## import sample data dem <- system.file("extdata/DEM.TIF", package = "satellite") dem <- trim(projectRaster(raster(dem), crs = "+init=epsg:4326")) ## current solar incidence angle solarIncidenceAngle(Sys.time(), dem, formula = "Spencer", unit = "degrees") ```