An apparatus for marking predetermined known overhead positional locations within a coordinate space, for viewing by an image acquisition system. The apparatus comprises a plurality of marker tags, grouped in one or more rows, each row having an axis, each row being supported by a row support. Each marker tag comprises an optically opaque, dark colored corrugated substrate, substantially rectangular in shape. A label having a unique machine-readable barcode symbology printed thereon is positioned centrally on the substrate so that a dark colored border of the substrate surrounds the label. Each row support comprises a first support cord and a second support cord. The first support cord supports a first lateral edge of the marker tags in a row group in a fixed, spaced-apart positional arrangement. The second support cord supports the second lateral edge of the marker tags in the row in a slidable support arrangement.