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<table width="100%" summary="page for grid.convert {grid}"><tr><td>grid.convert {grid}</td><td style="text-align: right;">R Documentation</td></tr></table>

<h2> Convert Between Different grid Coordinate Systems </h2>

<h3>Description</h3>

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

<h3>Usage</h3>

<pre>
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)
</pre>

<h3>Arguments</h3>

<table summary="R argblock">
<tr valign="top"><td><code>x</code></td>
<td>
<p> A unit object. </p>
</td></tr>
<tr valign="top"><td><code>unitTo</code></td>
<td>
<p> The coordinate system to convert the unit to.
See the <code><a href="unit.html">unit</a></code> function for valid coordinate systems.</p>
</td></tr>
<tr valign="top"><td><code>axisFrom</code></td>
<td>
<p> Either <code>"x"</code> or <code>"y"</code> to indicate
whether the unit object represents a value in the x- or
y-direction. </p>
</td></tr>
<tr valign="top"><td><code>typeFrom</code></td>
<td>
<p> Either <code>"location"</code> or <code>"dimension"</code>
to indicate whether the unit object represents a location or a
length. </p>
</td></tr>
<tr valign="top"><td><code>axisTo</code></td>
<td>
<p> Same as <code>axisFrom</code>, but applies to the unit object
that is to be created. </p>
</td></tr>
<tr valign="top"><td><code>typeTo</code></td>
<td>
<p> Same as <code>typeFrom</code>, but applies to the unit object
that is to be created. </p>
</td></tr>
<tr valign="top"><td><code>valueOnly</code></td>
<td>
<p> A logical indicating.  If <code>TRUE</code> then
the function does not return a unit object, but rather only the
converted numeric values. </p>
</td></tr>
</table>

<h3>Details</h3>

<p>The <code>convertUnit</code> function allows for general-purpose
conversions.  The other four functions are just more convenient
front-ends to it for the most common conversions.
</p>
<p>The conversions occur within the current viewport.
</p>
<p>It is not currently possible to convert to all valid coordinate systems
(e.g., &quot;strwidth&quot; or &quot;grobwidth&quot;).  I'm not sure if all of these
are impossible, they just seem implausible at this stage.
</p>
<p>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
<code>unit(1, "inches")</code> rather than something like
<code>unit(0.134, "native")</code>.
</p>
<p>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.
</p>

<h3>Value</h3>

<p>A unit object in the specified coordinate system
(unless <code>valueOnly</code> is <code>TRUE</code> in which case
the returned value is a numeric).
</p>

<h3>Warning</h3>

<p>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: <code>oneinch &lt;- convertUnit(unit(1, "inches"),
    "native")</code>.  Now if I resize the device, the unit object in
oneinch no longer corresponds to a physical length of 1 inch.
</p>

<h3>Author(s)</h3>

<p> Paul Murrell </p>

<h3>Examples</h3>

<pre>
## 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")
</pre>

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