<html><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">I tried clipping, but there's something I don't understand. In the example below, I first want to plot the surface<div>z=-xy, but only inside the cylinder x^2 +y^2 \leq 2.25. I used the circle centered at the origin with radius 1.5 as the clipping curve. Then I plotted what should be the boundary curve for this surface, using \parametricplot3D.</div><div>The output is attached. Why the discrepancy?</div><div><br></div><div>Example based on Herbert's example from 11/24/2008:</div><div><br></div><div><div><span class="Apple-tab-span" style="white-space:pre"> </span>\begin{pspicture}(-5,-9.5)(5,3)</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>\psset{unit=2}</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>\pstThreeDCoor[xMin=-2, xMax=2, yMin=-2,yMax=2, zMin=0, zMax=2]</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>\begin{psclip}{%</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>\pstThreeDCircle[linestyle=none](0,0,0)(1.5,0,0)(0,1.5,0)</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>}</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>\psplotThreeD[drawStyle=xyLines](-2,2)(-2,2){%</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>x y mul neg%</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>}</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>\end{psclip}</div><div><span class="Apple-tab-span" style="white-space:pre"> </span></div><div><span class="Apple-tab-span" style="white-space:pre"> </span>\parametricplotThreeD[linewidth=1.2pt, xPlotpoints=200](0,360){%</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>1.5 t cos mul %</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>1.5 t sin mul %</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>t cos t sin mul 1.5 mul neg%</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>}</div><div><span class="Apple-tab-span" style="white-space:pre"> </span></div><div><span class="Apple-tab-span" style="white-space:pre"> </span>\end{pspicture}</div><br></div><div></div></body></html>