Area measures

Several functions in SPATA2 have arguments that take area input. To specifically refer to an area the unit must be specified. There are three ways to create valid input for these arguments.

To test if the input is a valid distance measure use is_area().

Pixel and undefined units

There are two valid input options to specify an area in pixel:

• numeric: Single numeric values, e.g. arg_input = c(2, 3.554, 69, 100.67). If no unit is specified the input will be interpreted as pixels.

• character: Suffixed with 'px', e.g. arg_input = c('2px', '3.554px', '69px', '100.67px')

Note: The unit pixel and its abbreviaton 'px' is also used for numeric values which refer to area measures without any unit at all.

Furthermore, the unit pixel (px) is used for distances as well as for areas. If pixel refers to a distance the pixel side length is meant. If pixel refers to an area the number of pixels is meant.

According to the Systeme international d`unites (SI)

Specifying areas in SI units e.g. arg_input = c('2mm2', '4mm2') etc. requires the input to be a character as the unit must be provided as suffix. Between the numeric value and the unit must be no empty space! Valid suffixes can be obtained using the function validUnitsOfAreaSI().

As vectors of class unit

Behind the scenes SPATA2 works with the units package. Input is converted into vectors of class units. Therefore, input can be directly provided this way: arg_input = units::set_unit(x = c(2,4), value = 'mm2') Note that pixel is not a valid unit in the units package. If you want to specify the input in pixel you have to use input option 1. In pixel.

See also

Click here for an elaboration on distance measures in SPATA2.