You can't emulate a 4225 with xterm. Xterm only emulates a 4014 terminal or similar. These terminals were able to draw basic text and lines on a ~4096x3000 display in a plotter like fashion.
A 4225, as far as I remember, was supporting segmented 2D vector graphics, colors, curves, areas, bitmaps and so on. It was perhaps also supporting 3D (4115 and 4125 certainly did).
You might have a look at this commercial product (I have no experience with it though): http://www.fastpoint.com/products/emutek.html