santandermetgroup / convertr

A climate4R package for unit conversion and variable derivation

convertR: A climate4R package for unit conversion and variable derivation

convertR is an R package performing unit conversion and variable derivation using the climate4R Common Data Model.

Installation and requirements

Physical quantity handling is done via the Unidata's UDUNITS-2 software libraries, tailoring the functionalities of the R package udunits2 to the climate4R framework. Thus, the C-based UDUNITS-2 package must be installed in your system prior to package installation (link to installation instructions).

Then, install_github can be used:

devtools::install_github("SantanderMetGroup/convertR")

Unit conversion

The function udConvertGrid is used for unit conversion. An example follows:

library(convertR)
data("ps.iberia")
transformeR::getGridUnits(ps.iberia)
## [1] "Pascals"
range(ps.iberia$Data)
## [1]  86657.5 105690.0
ps.mmHg <- udConvertGrid(ps.iberia, new.units = "mmHg")
transformeR::getGridUnits(ps.mmHg)
## [1] "mmHg"
range(ps.mmHg$Data)
## [1] 649.9846 792.7401

Derivation of physical quantities

In the following table the available variable derivations are summarized, including the input variables. The nomenclature of the input variables to calculate the derivations is according to the climate4R vocabulary (see loadeR::c4R.vocabulary())

The (*) symbol indicates that the function is planned but not yet available.

function	Definition	psl	ps	tas	dpds	tdps	zgs	huss	hurs	rsds	rlds
psl2ps	Sea-level pressure to surface pressure	X		X			X
ps2psl	Surface pressure to sea-level pressure		X	X			X
rad2cc	Radiation to cloud cover									X	X
huss2hurs	Specific humidity to relative humidity		X	X				X
hurs2huss	Relative humidity from specific humidity		X	X					X
tas2ws	Saturation vapor pressure from temperature		X	X
hurs2w	Water vapor mixing ratio from relative humidity		X	X					X
dpds2hurs*	Relative humidity from dew-point depression		X	X	X
tdps2hurs	Relative humidity from dew-point temperature			X		X
hurs2tdps	Dew-point temperature from relative humidity			X					X
huss2pvp	Partial vapor pressure from specific humidity		X					X

The input variables do not require to be in specific units, as all the necessary unit conversions are internally undertaken by the unit converter utility.

convertr's Issues

precipitation conversion

Hi,

a very common conversion for precipitation is from kg/m2/s to mm/day. This currently fails as the water density is required to convert the kg into volume.

One final attempt to convert the units could be included for precipitation variables here:

convertR/R/udConvertGrid.R

Line 86 in 1b0d48c

if (!ud.are.convertible(u1[x], new.units[x])) stop("Non-convertible units \'ud.are.convertible\' returned FALSE)")

Simply by multiplying the units by the specific volume of water (1 l/kg):

> ud.convert(1, "kg/m^2/s", "mm/day")
Error in ud.convert(1, "kg/m^2/s", "mm/day") :
  Units kg/m^2/s and mm/day are not convertible
> ud.convert(1, "kg/m^2/s*l/kg", "mm/day")
[1] 86400