Theory and starting point

Starting point

The starting point of the project is the work of two previous students ( that studied a model for the relevation of undergound metal, which gives a basis for the development of the actual sensor. In particular they studied the electromagnetic wave reflected by the buried metal following the transmission of another electromagnetic wave. Our work focuses on the presentation, the transmission and localization of the data collected with this radar.

GPS Signal

The Global Positioning System (GPS) is a satellite-based radionavigation system owned by the United States government and operated by the United States Space Force. It is one of the global navigation satellite systems (GNSS) that provides geolocation and time information to a GPS receiver anywhere on or near the Earth where there is an unobstructed line of sight to four or more GPS satellites.

The way that the GPS finds his location is based on the principle of triangulation. Triangulation is a surveying method that measures the angles in a triangle formed by three survey control points. Using trigonometry and the measured length of just one side, the other distances in the triangle are calculated. Now if both positions of the other two are at known coordinates (which they are know because they are the satellites), we can determine the exact location of the GPS based upon those measurements. In reality, In order to determine your position, including your altitude, you actually need a minimum of four satellites:

  • Three satellites determine the X, Y, and Z coordinates.
  • The fourth one serves as a time reference.

Satellites send time and position information, and the data from multiple satellites are used to determine the location in three dimensions, as well as exact time. GPS modules do most of the hard work, extracting strings of data from multiple satellites, decoding it, and formatting the results into text strings. The format of these messages can vary, but most modules use the NMEA 0183 standard. This is a comma-delimited text format that consists of rows of data referred to as “sentences”. The sentences are provided with an identifier, which itself consists of character patterns, allowing for several dozen string formats. Here are some examples:

  • $GPBOD – Bearing, origin to destination
  • $GPBWC – Bearing and distance to waypoint, great circle
  • $GPGGA – Global Positioning System Fix Data
  • $GPGLL – Geographic position, latitude / longitude
  • $GPGSA – GPS DOP and active satellites
  • $GPGSV – GPS Satellites in view
  • $GPHDT – Heading, True
  • $GPR00 – List of waypoints in currently active route
  • $GPRMA – Recommended minimum specific Loran-C data
  • $GPRMB – Recommended minimum navigation info
  • $GPRMC – Recommended minimum specific GPS/Transit data
  • $GPRTE – Routes
  • $GPTRF – Transit Fix Data
  • $GPSTN – Multiple Data ID
  • $GPVBW – Dual Ground / Water Speed
  • $GPVTG – Track made good and ground speed
  • $GPWPL – Waypoint location
  • $GPXTE – Cross-track error, Measured
  • $GPZDA – Date & Time

Polytechnic department of engineering and architecture

Università degli Studi di Udine