The location in the geographical sense is your own position on the earth's surface or in a suitable geometric reference system . Semantically synonymous are terms such as standpoint , own position or topocenter (from the Greek topos for place), to which other terms from various scientific disciplines come. The determination of the location is often referred to as localization or location determination . In particular, time , speed and direction can be viewed as part of location data.
The location is not only important for your own orientation , but is also the (local) zero point of the so-called topocentric coordinate system for measurements . In a broader sense - for example in astronomy or space travel - the location can also be on other celestial bodies .
A location can be specified in a number of different ways, including:
- by geographic coordinates or by means of GPS-determined waypoints
- relative to another point, e.g. B. "50 meters south of the town hall" or "west of the summit XY at about above sea level"
- in a local coordinate system, defined by reference point and orientation
- by distances or kilometers , e.g. B. "at river kilometer 123.4"
- by specifying an intersection or a street and house number
Absolute and relative location information
The following coordinate systems can be considered absolute:
- Geographical coordinates (latitude and longitude), based on the reference ellipsoid of the national survey or (for simplicity) a mean globe . They can be measured by various methods of location determination or taken from a map. Most of the time, latitude and longitude are given, but a complete location also includes altitude .
- GPS coordinates. In addition to the WGS84 system, UTM coordinates are also widely used.
- In technology: Country coordinates in meters, mostly as Gauß-Krüger coordinates x, y (northing / easting). They are derived from a surveying network and are the system of geodetic measuring points and the boundary points of all properties;
- Spatial coordinates (X, Y, Z) in a Cartesian (right-angled) coordinate system. In the geosciences they refer to the center of the earth , in astronomy and space travel to the barycenter of the solar system .
Relative location information is more common in everyday life and for location reports that are unprepared. In the case of urgency ( accident , imminent danger), the reliability of the location report in terms of clarity is important, but also accessibility in the transport network.
A relative specification can be related to
- a street or an object
- Address (house number, object)
- Distance from an intersection
- Direction and distance from a prominent building
- Traffic routes, bodies of water, details in the area
- Mileage (milestone, river kilometers)
- Distance from a prominent structure
- in the great outdoors: peaks, mountainsides, forest edges
Examples of directions:
- "In the extension from A to B"
- "Towards 9 o'clock" (= west)
- "Approx. a hand's breadth to the right of the parish church "(A hand's breadth on the outstretched arm of the observer covers an angle of ~ 10 °.)
Conversion of relative information
Most of the relative locations can be converted to absolute, for example
For the accuracy of location information
To find a point again, the necessary accuracy depends on the task at hand. While at reports of incidents or accidents, the uniqueness of the Location is important, must at measuring the accuracy of the position information approximately the measurement accuracy correspond.
Examples of accuracies
The value of an observation or measurement at an outdoor location usually also depends on the reliability of the location information. For observations in the wild, a location at around 100 m is usually appropriate, as is easily possible with a map .
The accuracies can be very different for technical and scientific tasks.
- Terrestrial targets depending on distance: measurement accuracy (in degrees) × distance / 57.3. As an example : an event in 10 km, direction estimated at 10 ° → 1.7 km (1 km location is sufficient).
- Measurement of boundary points in an alpine pasture area : Meter accuracy is sufficient if the cadastral plan only has a scale of 1: 2880 or 1: 5000.
- Measurement of a sewer if the height reference to the community is required: millimeters to centimeters.
- Astronomical angle measurements to ± 1 ″ → location information to at least ± 30 m (corresponds to 1 ″ from the center of the earth).
- A bright meteor (ball of fire), direction of 5 ° recorded (in the constellation XY) → location at least 5 km (a glowing meteor is 50–100 km away).
Methods for accurate terrestrial location information
In the case of higher demands, the method also depends on the purpose and the object to be measured.
- In geography , for geological recordings or for antenna locations: drawing off distances from the map , directional bearing to landmarks or cartometric measurements.
- In geodesy : Determination of the instrument position ( theodolite ) by angle and distance measurements to survey points, or DGPS with several receivers.
- Navigation : current position data (location, time, direction, speed, quality parameters) to determine course with GPS , inertial navigation , with radio beacons or through dead reckoning (direction + speed) plus drift
- Suitable aids can be magnetic measurements, satellite images or photogrammetry .
- Fast moving targets also require a corresponding time specification .
Exact positions are usually specified in a coordinate system that relates to a defined reference point or zero point. The most important of these systems are based on complex measurements, but are therefore an absolute, permanent frame of reference.
- Heribert Kahmen : surveying , 19th edition, published by De Gruyter.
- Axel Bark : Sailing license , 9th edition, Bielefeld 1982.
- Thomas Glatte : Development of operational real estate - Procurement & utilization of real estate in corporate real estate management , Springer Vieweg, Wiesbaden 2014, ISBN 978-3-658-05686-5
- Brockhaus (6 volumes), Wiesbaden 1959–1961.