# PSTricks: Projection of point and right angle (both twice)

Consider the following code:

\documentclass{article}

\usepackage{pst-solides3d}

\begin{document}

\begin{figure}[htbp]
\centering
\psset{unit = 0.7}
\begin{pspicture}(-8.1,-5.6)(8.7,17.7)
\pnodes%
(0,17.65){A}%
(0,0){B}%
(3.09,-3.43){C}%
(-8.02,1.24){D}%
(-2.59,-5.57){E}%
(8.64,-1.34){F}%
(1.97,4.23){G}
\pspolygon[linestyle = none, fillstyle = solid, fillcolor = gray!20](D)(E)(F)(G)
\psSolid[
object = new,
action = draw,
sommets =
0 -3 0  % punkt 1
-3  0 0  % punkt 2
0  3 0  % punkt 3
3  0 0  % punkt 4
0  0 6, % punkt 5
faces = {
[3 2 1 0] % side A
[4 0 3]   % side B
[4 3 2]   % side C
[4 2 1]   % side D
[4 1 0]   % side E
},
RotZ = 30
]
\psline(0,0.65)(0.45,0.2)(0.45,-0.5)
\psline(3,-2.85)(3.6,-2.63)(3.67,-3.25)
{\psset{linestyle = dotted, linecolor = red}
\psline(A)(B)
\psline(B)(C)
\psline(A)(C)}
{\psset{linestyle = none}
\pcline[offset = -8.5pt](D)(E)
\ncput{$g$}
\pcline[offset = -8pt](E)(F)
\ncput{$g$}
\pcline[offset = 7pt](0,12)(B)
\ncput{$h$}
\pcline[offset = 8pt](A)(F)
\ncput{$x$}}
\end{pspicture}
\end{figure}

\end{document} The output is as I would like but the coordinates of the two projections and the right angles are found by trial and error. (One problem with the manually approach being that if I rotate the pyramid, the drawing is no longer correct.)

How do I use the pst-solides3d package to draw he entire drawing without having to find the coordinates manually?

• Side note: what happened to the Hpyramide question? I thought it was interesting, but then it disappeared... – Marijn Jun 14 '18 at 14:33
• @Marijn The package is very old and I found pst-solides3d which seems more up to date and easier to use. – Svend Tveskæg Jun 14 '18 at 16:37

\documentclass[pstricks]{standalone}
\usepackage{pst-solides3d}
\begin{document}
\begin{pspicture}(-4,-2)(4,7)
\psset{viewpoint=100 10 20 rtp2xyz,Decran=100,lightsrc=viewpoint,solidmemory}
\psSolid[
object = new,
action = draw*,
sommets =
0 -3 0  % punkt 0
-3  0 0  % punkt 1
0  3 0  % punkt 2
3  0 0  % punkt 3
0  0 6, % punkt 4
faces = {
[3 2 1 0] % side A
[4 0 3]   % side B
[4 3 2]   % side C
[4 2 1]   % side D
[4 1 0]   % side E
}]
% equation face : 2x+2y+z-6=0
\psSolid[object=plan,
definition=normalpoint,name=face2,action=none,
args={1.5 1.5 0 [-1.5 -1.5 6 2 2 1 -90]},
showbase]
\psset{plan=face2}
\psProjection[object=rightangle,
args= 0 1 0 0 1 0]
\psPoint(0,0,6){S}
\psPoint(0,0,0){O}
\psPoint(1.5,1.5,0){H}
\psPoint(0,-3,0){A}
\psPoint(3,0,0){B}
\psPoint(0,3,0){C}
\psPoint(-3,0,0){D}
\psline[linestyle=dotted,linecolor=red](H)(S)
\psline[linestyle=dotted,linecolor=red](O)(S)
\psline[linestyle=dotted,linecolor=red](O)(H)
% equation x-y=0
\psSolid[object=plan,
definition=normalpoint,name=planmedian,action=none,
args={0 0 0 [1.5 1.5 0 1 -1 0 0]},showbase]
\psset{plan=planmedian}
\psProjection[object=rightangle,
args= 0 1 0 0 1 0]
\uput[dl](O){$O$}
\uput[d](H){$H$}
\uput[u](S){$S$}
\uput[l](A){$A$}
\uput[d](B){$B$}
\uput[r](C){$C$}
\uput[r](D){$D$}
\end{pspicture}
\end{document} • Really nice. How do I remove the arrows from the right angles so that I "only" have the small square? – Svend Tveskæg Jun 17 '18 at 10:37

Without the vectors for the rightangle plane (you should accept the other amswer!):

\begin{pspicture}(-4,-2)(4,7)
\psset{viewpoint=100 10 20 rtp2xyz,Decran=100,solidmemory}
\psSolid[
object = new,
action = draw*,
sommets =
0 -3 0  % punkt 0
-3  0 0  % punkt 1
0  3 0  % punkt 2
3  0 0  % punkt 3
0  0 6, % punkt 4
faces = {
[3 2 1 0] % side A
[4 0 3]   % side B
[4 3 2]   % side C
[4 2 1]   % side D
[4 1 0]   % side E
}]
% equation face : 2x+2y+z-6=0
\psSolid[object=plan,
definition=normalpoint,name=face2,action=none,
args={1.5 1.5 0 [-1.5 -1.5 6 2 2 1 -90]}]
\psProjection[object=rightangle,plan=face2,
args= 0 1 0 0 1 0]
\psPoint(0,0,6){S}
\psPoint(0,0,0){O}
\psPoint(1.5,1.5,0){H}
\psPoint(0,-3,0){A}
\psPoint(3,0,0){B}
\psPoint(0,3,0){C}
\psPoint(-3,0,0){D}
\psline[linestyle=dotted,linecolor=red](H)(S)
\psline[linestyle=dotted,linecolor=red](O)(S)
\psline[linestyle=dotted,linecolor=red](O)(H)
% equation x-y=0
\psSolid[object=plan,definition=normalpoint,name=planmedian,action=none,
args={0 0 0 [1.5 1.5 0 1 -1 0 0]}]
\psProjection[object=rightangle,args= 0 1 0 0 1 0,plan=planmedian]
\uput[dl](O){$O$}
\uput[d](H){$H$}
\uput[u](S){$S$}
\uput[l](A){$A$}
\uput[d](B){$B$}
\uput[r](C){$C$}
\uput[r](D){$D$}
\end{pspicture} 