# Survey point

Measuring point - Berlin center (2005)
Measuring point with place name

A survey point , or measurement point for short, is a point marked in a stable manner in the ground or on a building, which geodesists use as the starting or destination point for measurements .

However, the term is not defined uniformly. Sometimes it is understood more narrowly in the sense of a fixed point : "A point that is determined in terms of location and / or height and is usually permanently fixed, to which topographical recordings, engineering or property measurements are connected."

Measurement points are determined as trigonometric points (TP) by means of triangulation . Height control points are determined by geometric leveling .

## Measurement point in the sense of fixed point

Measurement points are differentiated according to fixed points of the position, height and gravity fixed point field. For fixed position points (LFP), coordinates are calculated in a position reference system and they are mostly suitable as a set-up point for a surveying tripod with theodolite . Height control points (HFP) are used to determine heights above sea level, while for gravity control points (SFP) information on the force of gravity is measured and calculated.

Triangulation point with pillar and sign "tripod"

With the increasing importance of GPS surveying , these previously separate fixed point fields are increasingly becoming three-dimensional fixed points thanks to suitable markings. A line of sight over long distances is no longer necessary today.

## Overview of the surveying points that have been created in Germany since around 1820

Altitude mark
• Geodetic fixed points of the national survey - with stable above and below ground markings and typical positional accuracies of 1–5 cm
• in particular points of a triangulation ( definition , a plate and TP pillar), measuring pillar with signpost,
• Geodetic height control points of the national survey - with stable above-ground markings or as underground definition (UF) and typical height accuracies of ± 0.1 to 1 mm
• Fixed points of another surveying network - with stable marking and accuracies between 0.1 mm and about 10 cm (depending on the network size and purpose),
• For example technical control networks, measurement consoles, ridge points in the mine or tunnel
• Points that have been measured with GPS over a long period of time or measurement consoles.

## Other stable marketed survey points

In the parlance of most geodesists, surveying points also count

• Well-defined, controlled "detail points" that are clearly defined and stabilized on buildings or at borders - for example house corners, wall and border points
• Well-defined, immovable points in nature - for example, marks on rock or on large blocks in geodynamics measurements on mountain slopes or glaciers
• Ground marks in solid road pavement or on sidewalks - mostly bolts or nails with the inscription "measurement point" or "measuring point"
• Screw marks or stably driven pegs , if possible with a notice peg or protective scaffolding
• Geodetic reference points for checking GPS receivers
• other permanently marketed items

## Points and measures in databases

In the age of IT , the measurement points are stored in databases for almost all work . In addition to names and coordinates , the "history of origin" and the relationship between the points are noted, so that the exact position of each measurement point can be updated at any time using new measurement data . Such measurements are mainly:

In geographic information systems , individual elements are often linked to survey points, for example in order to transform local coordinates into a higher-level reference system . The information about which points such links exist is usually stored in the geometry of the GIS element.