def create_pointing(self, event, label_text=None):
        """Plot the sky coverage of pointing at event.x,event.y on the canvas.

        """
        x = self.canvasx(event.x)
        y = self.canvasy(event.y)
        (ra, dec) = self.c2p((x, y))
        this_camera = Camera(ra=float(ra) * units.radian, dec=float(dec)*units.radian, camera=self.camera.get())

        ccds = numpy.radians(numpy.array(this_camera.geometry))
        items = []
        for ccd in ccds:
            if len(ccd) == 4:
                (x1, y1) = self.p2c((ccd[0], ccd[1]))
                (x2, y2) = self.p2c((ccd[2], ccd[3]))
                item = self.create_rectangle(x1, y1, x2, y2, stipple='gray25', fill=None)
            else:
                (x1, y1) = self.p2c((ccd[0] - ccd[2], ccd[1] - ccd[2]))
                (x2, y2) = self.p2c((ccd[0] + ccd[2], ccd[1] + ccd[2]))
                item = self.create_oval(x1, y1, x2, y2)
            items.append(item)
        label = {}
        if label_text is None:
            label_text = self.plabel.get()
        label['text'] = label_text
        label['id'] = self.label(this_camera.ra.radian, this_camera.dec.radian, label['text'])
        self.pointings.append({
            "label": label,
            "items": items,
            "camera": this_camera})
        self.current = len(self.pointings) - 1
        self.current_pointing(len(self.pointings) - 1)
Plot the sky coverage of pointing at event.x,event.y on the canvas.