\begin{pspicture}(-2.3,-0.8)(2.3,1.5) \psset{unit=.3cm} \psset{viewpoint=-1 -1 1} \ThreeDput[normal=0 0 1]{\psgrid(-3,-3)(6,6)} \ThreeDput[normal=-1 0 0](0,4,0){\psframe*[linecolor=yellow](4,4)} \end{pspicture}