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<a name="Interpolation-on-Scattered-Data"></a>
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Previous: <a rel="previous" accesskey="p" href="Convex-Hull.html#Convex-Hull">Convex Hull</a>,
Up: <a rel="up" accesskey="u" href="Geometry.html#Geometry">Geometry</a>
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<h3 class="section">30.4 Interpolation on Scattered Data</h3>
<p>An important use of the Delaunay tessellation is that it can be used to
interpolate from scattered data to an arbitrary set of points. To do
this the N-simplex of the known set of points is calculated with
<code>delaunay</code>, <code>delaunay3</code> or <code>delaunayn</code>. Then the
simplices in to which the desired points are found are
identified. Finally the vertices of the simplices are used to
interpolate to the desired points. The functions that perform this
interpolation are <code>griddata</code>, <code>griddata3</code> and
<code>griddatan</code>.
<!-- griddata scripts/geometry/griddata.m -->
<p><a name="doc_002dgriddata"></a>
<div class="defun">
— Function File: <var>zi</var> = <b>griddata</b> (<var>x, y, z, xi, yi, method</var>)<var><a name="index-griddata-2814"></a></var><br>
— Function File: [<var>xi</var>, <var>yi</var>, <var>zi</var>] = <b>griddata</b> (<var>x, y, z, xi, yi, method</var>)<var><a name="index-griddata-2815"></a></var><br>
<blockquote>
<p>Generate a regular mesh from irregular data using interpolation.
The function is defined by <var>z</var><code> = f (</code><var>x</var><code>, </code><var>y</var><code>)</code>.
Inputs <var>x</var><code>, </code><var>y</var><code>, </code><var>z</var> are vectors of the same length
or <var>x</var><code>, </code><var>y</var> are vectors and <var>z</var> is matrix.
<p>The interpolation points are all <code>(</code><var>xi</var><code>, </code><var>yi</var><code>)</code>. If
<var>xi</var>, <var>yi</var> are vectors then they are made into a 2-D mesh.
<p>The interpolation method can be <code>"nearest"</code>, <code>"cubic"</code> or
<code>"linear"</code>. If method is omitted it defaults to <code>"linear"</code>.
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<p class="noindent"><strong>See also:</strong> <a href="doc_002ddelaunay.html#doc_002ddelaunay">delaunay</a>.
</p></blockquote></div>
<!-- griddata3 scripts/geometry/griddata3.m -->
<p><a name="doc_002dgriddata3"></a>
<div class="defun">
— Function File: <var>vi</var> = <b>griddata3</b> (<var>x, y, z, v, xi, yi, zi, method, options</var>)<var><a name="index-griddata3-2816"></a></var><br>
<blockquote>
<p>Generate a regular mesh from irregular data using interpolation.
The function is defined by <var>v</var><code> = f (</code><var>x</var><code>, </code><var>y</var><code>, </code><var>z</var><code>)</code>.
The interpolation points are specified by <var>xi</var>, <var>yi</var>, <var>zi</var>.
<p>The interpolation method can be <code>"nearest"</code> or <code>"linear"</code>.
If method is omitted it defaults to <code>"linear"</code>.
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<p class="noindent"><strong>See also:</strong> <a href="doc_002dgriddata.html#doc_002dgriddata">griddata</a>, <a href="doc_002dgriddatan.html#doc_002dgriddatan">griddatan</a>, <a href="doc_002ddelaunayn.html#doc_002ddelaunayn">delaunayn</a>.
</p></blockquote></div>
<!-- griddatan scripts/geometry/griddatan.m -->
<p><a name="doc_002dgriddatan"></a>
<div class="defun">
— Function File: <var>yi</var> = <b>griddatan</b> (<var>x, y, xi, method, options</var>)<var><a name="index-griddatan-2817"></a></var><br>
<blockquote>
<p>Generate a regular mesh from irregular data using interpolation.
The function is defined by <var>y</var><code> = f (</code><var>x</var><code>)</code>.
The interpolation points are all <var>xi</var>.
<p>The interpolation method can be <code>"nearest"</code> or <code>"linear"</code>.
If method is omitted it defaults to <code>"linear"</code>.
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<p class="noindent"><strong>See also:</strong> <a href="doc_002dgriddata.html#doc_002dgriddata">griddata</a>, <a href="doc_002ddelaunayn.html#doc_002ddelaunayn">delaunayn</a>.
</p></blockquote></div>
<p>An example of the use of the <code>griddata</code> function is
<pre class="example"> rand("state",1);
x=2*rand(1000,1)-1;
y=2*rand(size(x))-1;
z=sin(2*(x.^2+y.^2));
[xx,yy]=meshgrid(linspace(-1,1,32));
griddata(x,y,z,xx,yy);
</pre>
<p class="noindent">that interpolates from a random scattering of points, to a uniform
grid.
The output of the above can be seen in <a href="fig_003agriddata.html#fig_003agriddata">fig:griddata</a>.
<div class="float">
<a name="fig_003agriddata"></a><div align="center"><img src="griddata.png" alt="griddata.png"></div>
<p><strong class="float-caption">Figure 30.6: Interpolation from a scattered data to a regular grid</strong></p></div>
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