The apparatus has an x-ray source that emits an x-ray cone beam through a tubular, x-ray-blocking guide to a planar template with a small pinhole to produce a pencil beam. A list of candidates headed by the nearest constellation point and with remaining candidates presorted by proximity to the head is selected, for each such quantized estimate based on constellation point selections for previously processed layers. The hem seal may also form a hem at the open mouth of the tie bag.