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<p>The help says that splin2d generates bicubic patches, so presumably it's not linear interpolation.</p>
<p>On 2017-03-25 00:24, paul.carrico@free.fr wrote:</p>
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<div class="pre" style="margin: 0; padding: 0; font-family: monospace;">Hi All<br /><br />To go further in 2D/3D interpolation as I started in my previous emails, I built the example here after.</div>
<div class="pre" style="margin: 0; padding: 0; font-family: monospace;"> </div>
<div class="pre" style="margin: 0; padding: 0; font-family: monospace;">As suggested, I had a look to</div>
<div class="pre" style="margin: 0; padding: 0; font-family: monospace;">- cshep2d but but seems can not be used here (dimensions issue)</div>
<div class="pre" style="margin: 0; padding: 0; font-family: monospace;">- splin2d + interp2d</div>
<div class="pre" style="margin: 0; padding: 0; font-family: monospace;"> </div>
<div class="pre" style="margin: 0; padding: 0; font-family: monospace;">In the later case, Am I right to say that splin2d "cross-sections" the surface in order to define the "best spline" passing through the nodes (in the cross section obviously), then the interpolation/calculation is basically using this new 2D function, right ?</div>
<div class="pre" style="margin: 0; padding: 0; font-family: monospace;"> </div>
<div class="pre" style="margin: 0; padding: 0; font-family: monospace;">if so this is not a linear interpolation between 2 nodes (as I expect), isn't it?</div>
<div class="pre" style="margin: 0; padding: 0; font-family: monospace;"> </div>
<div class="pre" style="margin: 0; padding: 0; font-family: monospace;"> </div>
<div class="pre" style="margin: 0; padding: 0; font-family: monospace;"> </div>
<div class="pre" style="margin: 0; padding: 0; font-family: monospace;">Paul</div>
<div class="pre" style="margin: 0; padding: 0; font-family: monospace;"> </div>
<div class="pre" style="margin: 0; padding: 0; font-family: monospace;">############################################</div>
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<pre><span>mode</span><span>(</span><span>0</span><span>)</span>
<span>n</span><span>=</span><span>10</span><span>;</span>
<span>x</span> <span>=</span> <span>linspace</span><span>(</span><span>0</span><span>,</span><span>300</span><span>,</span><span>(</span><span>n</span><span>+</span><span>1</span><span>)</span><span>)</span><span>'</span><span>;</span> <span>// abscissa</span>
<span>t</span> <span>=</span> <span>[</span><span>0</span> <span>25</span> <span>100</span><span>]</span><span>;</span> <span>// temperature</span>
<span>z</span> <span>=</span> <span>20</span><span>*</span><span>rand</span><span>(</span><span>(</span><span>n</span><span>+</span><span>1</span><span>)</span><span>,</span><span>3</span><span>)</span><span>;</span> <span>// ordinate</span>
<span>// Nota : we must have the same number of data for both x and z</span>
<span>// plot3d</span>
<span>clf</span><span>(</span><span>)</span>
<span>a</span><span>=</span><span>get</span><span>(</span><span>"</span><span>current_axes</span><span>"</span><span>)</span><span>;</span>
<span>a</span><span>.</span><span>x_label</span><span>;</span> <span>x_label</span><span>=</span><span>a</span><span>.</span><span>x_label</span><span>;</span> <span>x_label</span><span>.</span><span>text</span><span>=</span><span>"</span><span> X abscissa</span><span>"</span><span>;</span>
<span>a</span><span>.</span><span>y_label</span><span>;</span> <span>y_label</span><span>=</span><span>a</span><span>.</span><span>y_label</span><span>;</span> <span>y_label</span><span>.</span><span>text</span><span>=</span><span>"</span><span> Temperature T</span><span>"</span><span>;</span>
<span>a</span><span>.</span><span>z_label</span><span>;</span> <span>z_label</span><span>=</span><span>a</span><span>.</span><span>z_label</span><span>;</span> <span>z_label</span><span>.</span><span>text</span><span>=</span><span>"</span><span> y ordinate</span><span>"</span><span>;</span>
<span>plot3d</span><span>(</span><span>x</span><span>,</span><span>t</span><span>,</span><span>z</span><span>)</span>
<span>// Nota: if I do a cross section normal to XoZ plane, I</span><span>'</span><span>ve the basic curve z=f(x,T)) -> seems correct</span>
<span>// interpolation</span>
<span>xp</span> <span>=</span> <span>[</span><span>22</span> <span>103</span> <span>236</span><span>]</span><span>'</span>
<span>tp</span> <span>=</span> <span>[</span><span>5</span> <span>56</span> <span>85</span><span>]</span><span>'</span>
<span>[</span><span>Xp</span><span>,</span><span>Tp</span><span>]</span> <span>=</span> <span>ndgrid</span><span>(</span><span>xp</span><span>,</span><span>tp</span><span>)</span></pre>
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