<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">The code<div>%%%%%%%%%%%%%%%%%%%%%%%%%%%%</div><div><div>\usepackage{pst-solides3d,pst-plot,pst-3dplot,amsmath}</div><div>\begin{document}</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>\begin{pspicture*}(-2.5,-2.0)(2.5,3.5)%<span class="Apple-tab-span" style="white-space:pre"> </span></div><div><span class="Apple-tab-span" style="white-space:pre"> </span>\psset{unit=0.25,lightsrc=40 50 50,viewpoint=18 40 25 rtp2xyz,solidmemory}</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>\psSolid[object=plan,%<span class="Apple-tab-span" style="white-space:pre"> </span>definition of plane @ z=0</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>definition=equation,args={[0 0 1 0]},</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>base=-2.5 2.5 -2.5 2.5,</div><div><span class="Apple-tab-span" style="white-space:pre"> </span> <span class="Apple-tab-span" style="white-space:pre"> </span>fillcolor=gray!30,</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>name=zplane,</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>ngrid=10 10, grid,</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>action=draw**,</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>\defFunction{zcurve}(t){t cos 2 mul}{t sin}{}%</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>\psProjection[object=courbeR2,%<span class="Apple-tab-span" style="white-space:pre"> </span>slice @ x=0 (front part)</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>r=0.8,</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>linecolor=black,linewidth=0.8pt, </div><div><span class="Apple-tab-span" style="white-space:pre"> </span>plan=zplane,</div><div><span class="Apple-tab-span" style="white-space:pre"> </span> <span class="Apple-tab-span" style="white-space:pre"> </span>range=0 360,</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>resolution=720, visibility=false,</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>function=zcurve,</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>action=draw**</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>\composeSolid</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>%</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>\axesIIID[linecolor=darkgray, linewidth=1pt, showOrigin=false]%</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>(0,0,0)(3.0,3.0,3.0)<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><div>%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%</div><div>leads to the picture below. I don't understand why the projected ellipse does not show up.</div><div></div></div></body></html>