def limits(self,x1,x2,y1,y2):
        """Set the coordinate boundaries of plot"""
        import math
        self.x1=x1
        self.x2=x2
        self.y1=y1
        self.y2=y2
        self.xscale=(self.cx2-self.cx1)/(self.x2-self.x1)
        self.yscale=(self.cy2-self.cy1)/(self.y2-self.y1)

	ra1=self.x1
	ra2=self.x2
	dec1=self.y1
	dec2=self.y2
        (sx1,sy2)=self.p2c((ra1,dec1))
        (sx2,sy1)=self.p2c((ra2,dec2))
	
        
        self.config(scrollregion=(sx1-self.lgutter,sy1+self.bgutter,sx2+self.rgutter,sy2-self.tgutter))