More information
The satellites available for positioning are summarized under the term GNSS (Global Navigation Satellite System). It consists of the systems GPS (USA), GLONASS (Russia), Beidou (China) and Galileo (Europe). Modern GNSS receivers can already use several of these systems at the same time.
The GNSS module in your smartphone receives signals (codes) from several satellites. The distance between the respective satellite and the device is derived from these signals. If the distances to at least 4 satellites are known it will be possible to calculate the position of the receiver. The accuracy of the position of your smartphone is usually better than 10 meters.
GNSS is also used for surveying work with an accuracy in the cm-range, for this work one needs more efficient GNSS receivers as well as special measurement and evaluation methods.
The GNSS receiver shows the position in form of coordinates (latitude and longitude). They usually refer to the worldwide coordinate system WGS84 (World Geodetic System 1984). The system has its origin at the center of gravity of the earth.
The longitude L counts from the prime meridian in Greenwich/UK eastward positive and westward negative (-180°W smaller than L smaller than 180°O). The latitude B counts from the equator northward positive and southward negative (-90°S smaller than B smaller than 90°N). Due to its geographic position Austria's (A) coordinate values are both positive.
The coordinates measured by the GNSS receiver (longitude and latitude) can be projected on a cylinder touching the earth via a map projection. On its unrolled surface, the map, the northing is counted in the North-South direction from the equator and the easting in the East-West direction from the central meridian.
To reduce distortions to a minimum, only 6° broad meridian bands are used for the projection. Internationally the 60 bands are clearly defined and called zones. Austria is completely covered by the zones 32 and 33 with the central meridians 9° and 15° East of Greenwich.
In the coordinate system WGS84 the height is defined as the vertical distance to the surface of the WGS84 ellipsoid (ellipsoidal height Hell).
Thes sea height (H) is defined as the vertical distance to a mean sea level. This reference surface the mean sea level that is called a geoid.
The heights above sea level are derived from measured height differences of the precise leveling (= high precision height measurement) and the gravity acceleration at this point.
The gravity is measured with special measuring instruments, the gravimeters. The value of the gravity varies on the earth due to the location, height and the density of the rock (earth crust structure) between 9,78m/s² at the equator and 9,83m/s² at the pol.
The difference of the mean sea level to the ellipsoidal height is called geoid undulation (N).
The value amounts to 40-50 meters in Austria.
A smartphone does, if possible, not only use satellite data for positioning. Assisted Global Positioning System (A-GPS) uses additional information such as the current radio cell of the smartphone or a current WLAN access point. The data of the orbits of the satellite are stored in the device as well. Thus it is possible to get the position more quickly and free of interruptions, even when less than 4 satellites are available.
- Scan the QR code on the metal plate of the control point and follow the indicated link.
- On your smartphone a web browser opens with a map.
- Hold your smartphone above the middle of the metal plate and the map will show you how accurately your smartphone shows your position.
If you use a mobile navigation device or a respective app on your smartphone you will be able to compare your measured coordinate values to the coordinates of the control point.
Please ensure that your device settings comply with the specifications on the metal plate of the control point (e.g. WGS84, UTM).