concept_distance_measure.RdSeveral functions in SPATA2 have arguments that take distance input. To specifically refer to a distance 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_dist().
There are two valid input options to specify the distance 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 distance 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.
Specifying distances in SI units e.g. arg_input = c('2mm', '4mm') 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 validUnitsOfLengthSI().
unitBehind 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 = 'mm')
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.
Click here for an elaboration
on area measures in SPATA2.