Right angle in 3D-pstricks

I’d like to draw a right angle in a 3D-pstricks-graphic. I can’t find a way to do that. This is what I want to do (but in 3D):

Here is my code:

documentclass{standalone}
usepackage[T1]{fontenc}
usepackage[utf8]{inputenc}
usepackage[ngerman]{babel}
usepackage{pst-all}
usepackage{pst-3dplot}

begin{document}

psset{coorType=2}
begin{pspicture}(-3,-3.1)(3.5,3.5)
pstThreeDCoor[xMin = -3, xMax = 3, yMin = -3, yMax = 3, zMin = -3, zMax = 3, arrows = ->, linecolor=black]
pstThreeDTriangle[fillcolor=yellow,fillstyle=solid,linecolor=black,opacity=0.5](2,0,0)(0,2.5,0)(0,0,1)
pstThreeDLine[linestyle=dashed](0.489361,0.691489,0.478723)(1.5,1.5,2.5)
pstThreeDDot(1.5,1.5,2.5)
pstThreeDPut(1.5,1.8,2.5){$P$}
pstThreeDDot(0.489361,0.691489,0.478723)
pstThreeDPut(0.489361,0.991489,0.478723){$P'$}
pstThreeDDot(2,0,0)
pstThreeDPut(2,-0.3,0){2}
pstThreeDDot(0,2.5,0)
pstThreeDPut(0,2.5,0.3){2.5}
pstThreeDDot(0,0,1)
pstThreeDPut(0,-0.3,1){1}
end{pspicture}

end{document}

In the picture you can see what I have got. I need to show two right angles so the projection is better visible.

Is there an equivalent of psarc in 3D?

pstThreeDEllipse[beginAngle=0,endAngle=90](0,0,1)(0.5,0,-0.25)(0,0.625,-0.25)
pstThreeDDot(0.3,0.3,0.85)

 documentclass{standalone}
 usepackage[T1]{fontenc}
 usepackage[utf8]{inputenc}
 usepackage[ngerman]{babel}
 usepackage{pst-all}
 usepackage{pst-3dplot}

 begin{document}

 psset{coorType=2}
 begin{pspicture}(-3,-3.1)(3.5,3.5)
 pstThreeDCoor[xMin = -3, xMax = 3, yMin = -3, yMax = 3, zMin = -3, zMax = 3, arrows = ->, linecolor=black]
    ThreeDput[normal=1.3 1 3](0,0,1.66){%
    pspolygon[fillcolor=yellow,fillstyle=solid,linecolor=black,opacity=0.8]%
     (0,0)(-3,0)(0,-3)
     psarc{-}(0,0){0.6}{-180}{-90}
     psdot[dotsize=1mm](-0.2,-0.2)
     psdot[dotsize=2mm](0,0)
     psdot[dotsize=2mm](-3,0)
     psdot[dotsize=2mm](0,-3)}
 pstThreeDLine[linestyle=dashed](0.33,0.5,0.5)(1.5,1.5,2.5)
 pstThreeDDot(1.5,1.5,2.5)
 pstThreeDPut(1.5,1.8,2.5){$P$}
 pstThreeDDot(0.33,0.5,0.5)
 pstThreeDPut(0.33,0.8,0.5){$P'$}
 rput[r](-0.2,1.4){1}
 rput[r](-0.5,-0.4){2}
 rput[b](2.6,0.1){2.5}
end{pspicture}

end{document}