Source PostScript (elltransform.pps)

%% syntaxe : [ellipse] ell2pol --> [A A' B B']
/ell2pol {
4 dict begin
   aload pop
   /ang exch def
   /b exch def
   /a exch def
   /I defpoint
   [
      I a neg 0 addv
      I 0 b neg addv
      I a 0 addv
      I 0 b addv
   ]
   {I ang rotatepoint} papply
end
} def

%% syntaxe : [A B A' B'] pol2ell --> [ellipse]
/pol2ell {
5 dict begin
   aload pop 
   /B' defpoint
   /A' defpoint
   /B defpoint
   /A defpoint 
   [
      A A' milieu
      2 copy /I defpoint
      A A' distance 2 div
      B B' distance 2 div
      A A' angle 
   ]
end
} def

%% syntaxe : ell u translateell --> ell'
/translateell {
2 dict begin   
   /uy exch def
   /ux exch def
   ell2pol
   {ux uy translatepoint} papply
   pol2ell
end
} def

%% syntaxe : ell I alpha rotateell --> ell'
/rotateell {
2 dict begin   
   /alpha exch def
   /I defpoint
   ell2pol
   {I alpha rotatepoint} papply
   pol2ell
end
} def

%% syntaxe : ell I alpha homell --> ell'
/homell {
2 dict begin   
   /alpha exch def
   /I defpoint
   ell2pol
   {I alpha hompoint} papply
   pol2ell
end
} def

%% syntaxe : ell I symell --> ell'
/symell {
1 dict begin   
   /I defpoint
   ell2pol
   {I sympoint} papply
   pol2ell
end
} def

%% syntaxe : ell D axesymell --> ell'
/axesymell {
1 dict begin   
   /D defdroite
   ell2pol
   {D axesympoint} papply
   pol2ell
end
} def