Geodetic monuments for GPS campaigns ensure that the surveyed point is directly coupled to the solid earth. The marks are typically flush or near the surface for stability, minimal visibility, security, and low cost. During campaigns, the GPS antenna is temporarily mounted above the monument using one of various set-ups such as tripods, spike mounts, leveling mounts, or monument specific mounts. In every case, the antenna must be precisely centered and leveled, and the antenna height above the monument must be measured or known. Ideally, GPS monuments are placed in bedrock.