Glossary for Geospatial Science

tie point:� A point that is co-located on two raster objects that have an overlapping geographic extent.� Tie points are used in the manual mosaic process to establish the relationship between adjacent pieces of the mosaic that provide no absolute ground control information, but do show some common ground feature in each piece.� For example, multiple frames of airvideo can be tied together with tie points (farm buildings, field corners, bushes, rock outcroppings, bends in streams) even if the map coordinates are not known for such features.� Then, the map calibration for the entire sequence can be established from control points sparsely located in the mosaic sequence (such as road intersections) for which the map coordinates are known.� (See also: control point.)