R: Convert Between Different grid Coordinate Systems

grid.convert {grid} | R Documentation

## Convert Between Different grid Coordinate Systems

### Description

These functions take a unit object and convert it to an equivalent unit object in a different coordinate system.

### Usage

    convertX(x, unitTo, valueOnly = FALSE)
    convertY(x, unitTo, valueOnly = FALSE)
    convertWidth(x, unitTo, valueOnly = FALSE)
    convertHeight(x, unitTo, valueOnly = FALSE)
    convertUnit(x, unitTo,
                 axisFrom = "x", typeFrom = "location",
                 axisTo = axisFrom, typeTo = typeFrom,
                 valueOnly = FALSE)

### Arguments

`x` | A unit object.
`unitTo` | The coordinate system to convert the unit to. See the `unit` function for valid coordinate systems.
`axisFrom` | Either `"x"` or `"y"` to indicate whether the unit object represents a value in the x- or y-direction.
`typeFrom` | Either `"location"` or `"dimension"` to indicate whether the unit object represents a location or a length.
`axisTo` | Same as `axisFrom`, but applies to the unit object that is to be created.
`typeTo` | Same as `typeFrom`, but applies to the unit object that is to be created.
`valueOnly` | A logical indicating. If `TRUE` then the function does not return a unit object, but rather only the converted numeric values.

### Details

The `convertUnit` function allows for general-purpose conversions. The other four functions are just more convenient front-ends to it for the most common conversions.

The conversions occur within the current viewport.

It is not currently possible to convert to all valid coordinate systems (e.g., "strwidth" or "grobwidth"). I'm not sure if all of these are impossible, they just seem implausible at this stage.

In normal usage of grid, these functions should not be necessary. If you want to express a location or dimension in inches rather than user coordinates then you should simply do something like `unit(1, "inches")` rather than something like `unit(0.134, "native")`.

In some cases, however, it is necessary for the user to perform calculations on a unit value and this function becomes necessary. In such cases, please take note of the warning below.

### Value

A unit object in the specified coordinate system (unless `valueOnly` is `TRUE` in which case the returned value is a numeric).

### Warning

The conversion is only valid for the current device size. If the device is resized then at least some conversions will become invalid. For example, suppose that I create a unit object as follows: `oneinch <- convertUnit(unit(1, "inches"), "native")`. Now if I resize the device, the unit object in oneinch no longer corresponds to a physical length of 1 inch.

### Author(s)

Paul Murrell

### See Also

`unit`

### Examples

    ## A tautology
    convertX(unit(1, "inches"), "inches")
    ## The physical units
    convertX(unit(2.54, "cm"), "inches")
    convertX(unit(25.4, "mm"), "inches")
    convertX(unit(72.27, "points"), "inches")
    convertX(unit(1/12*72.27, "picas"), "inches")
    convertX(unit(72, "bigpts"), "inches")
    convertX(unit(1157/1238*72.27, "dida"), "inches")
    convertX(unit(1/12*1157/1238*72.27, "cicero"), "inches")
    convertX(unit(65536*72.27, "scaledpts"), "inches")
    convertX(unit(1/2.54, "inches"), "cm")
    convertX(unit(1/25.4, "inches"), "mm")
    convertX(unit(1/72.27, "inches"), "points")
    convertX(unit(1/(1/12*72.27), "inches"), "picas")
    convertX(unit(1/72, "inches"), "bigpts")
    convertX(unit(1/(1157/1238*72.27), "inches"), "dida")
    convertX(unit(1/(1/12*1157/1238*72.27), "inches"), "cicero")
    convertX(unit(1/(65536*72.27), "inches"), "scaledpts")

    pushViewport(viewport(width=unit(1, "inches"),
                           height=unit(2, "inches"),
                           xscale=c(0, 1),
                           yscale=c(1, 3)))
      ## Location versus dimension
      convertY(unit(2, "native"), "inches")
      convertHeight(unit(2, "native"), "inches")
      ## From "x" to "y" (the conversion is via "inches")
      convertUnit(unit(1, "native"), "native",
                   axisFrom="x", axisTo="y")
      ## Convert several values at once
      convertX(unit(c(0.5, 2.54), c("npc", "cm")),
                    c("inches", "native"))
    popViewport()
    ## Convert a complex unit
    convertX(unit(1, "strwidth", "Hello"), "native")

[Package grid version 3.5.1 Index]