struct object *straighten(obj, poly)
struct object *obj, *poly;
{
	struct object *strobj, *makemain(), *threshold();
	struct intervaldomain *idom,*makedomain();
	struct valuetable *vtbl,*makevaluetb();
	struct polygondomain *p, *ply, *makepolydmn();
	struct iwspace iwsp;
	struct gwspace gwsp;
	int strwidth,halfwidth,sline,mlines,i,*g;
	float x,y,sintheta,costheta;

	p = (struct polygondomain *) poly->idom;
	if (poly->type != 10 || p->type != 2) {
		fprintf(stderr,"not a type 2 polygon\n");
		exit(91);
	}
	mlines = p->nvertices;

	/*
	 * approximate mean width of object
	 * this is used as half-width of straightened object
	 */
	halfwidth = area(obj)/mlines;
	if (halfwidth > 10)
		halfwidth = 10;
	strwidth = 1 + 2*halfwidth;

	/*
	 * make a rectangular object with an empty grey table
	 */
	idom = makedomain(2,1,mlines,1,strwidth);
	vtbl = makevaluetb(1,1,mlines,0,NULL);
	strobj = makemain(1,idom,vtbl,NULL,obj);
	vtbl->original = strobj;
/* have to make grey-table one bigger than might be thought necessary
as somewhere there is a loss of sync !!!!!!!!!!!!!!!!!!!!!!!!!!!!!! */
	g = (int *) calloc(mlines*strwidth+1,sizeof(int));
	for (i=1; i<=mlines; i++) {
		makevalueline(vtbl,i,1,strwidth,g);
		g += strwidth;
	}

	/*
	 * start transformation
	 */
	initgreyscan(strobj,&iwsp,&gwsp);
	for (sline=1; sline<=mlines; sline++) {
		/*
	 	* get next column, line (x,y) in unit-spaced steps
	 	* along smoothed mid-points polygon, and local orientation.
	 	* sline is line number in straightened object
	 	*/
		setnextpoint(p,&x,&y,&sintheta,&costheta,sline);

		/*
		 *  rotate and fill rotated interval centred at x,y.
		 */
		nextgreyinterval(&iwsp);
		g = gwsp.grintptr;
		rotate(obj,x,y,sintheta,costheta,halfwidth,g);
	}
	/*
	 * threshold to remove unset points
	 */
	strobj = threshold(strobj,1);
	return(strobj);
}