I have a GNSS Quectel L76 module, I get coordinates from it and I want to know the accuracy of these coordinates, that is, the error in meters. How to do it?

    3 answers 3

    If we are talking about the direct processing of the NMEA protocol, it imparts the parameters of the degradation of accuracy:
    PDOP (Position Dilution of Precision) - reduction in accuracy by location - is transmitted in messages $ GPGSA, $ PGRMF
    HDOP (Horizontal Dilution of Precision) - reduction of accuracy in the horizontal plane - is transmitted in messages $ GPGSA, $ GPGGA
    VDOP (Vertical Dilution of Precision) - reduction of accuracy in the vertical plane - is transmitted in the message $ GPGSA
    TDOP (Time dilution of precision) - reduced accuracy in time - transmitted in the $ PGRMF message

    It is difficult to convert errors into meters. These are estimated values. To clarify this possibility, you should read the documentation for the receiver.

    UPD: Usually, for simplicity, HDOP is multiplied by the receiver error.

      To answer such questions, look good datasheets. Here for example, it is easy to be that accuracy is less than 2.5 meters .

      • Yes, I datashit him very well. But this figure is not quite clear to me. And I have seen in some forums how this number is multiplied by HDOP. But there is no explanation anywhere on this. - Vladislav
      • This number indicates that when the gps module goes into operation, the actual position will differ from the measured one by no more than 2.5 meters. - KoVadim

      The typical accuracy of determining the coordinates of GPS receivers in the horizontal plane is approximately 1-2 meters (subject to good visibility of the sky). The accuracy of determining the height above sea level is usually 2-5 times lower than the accuracy of determining the coordinates in the same conditions (ie, in ideal conditions, 2-10 meters).

      The level of reception of the signal from the satellites, and as a result, the accuracy of determining the coordinates, deteriorates under dense foliage of trees or due to very large clouds. Also, the normal reception of GPS signals can be damaged by interference from many terrestrial radio sources. However, the main factor affecting the decrease in GPS accuracy is the incomplete visibility of the sky. This is especially pronounced when a GPS receiver is located in a dense urban environment, when a significant part of the sky is hidden by nearby buildings, sheds and other obstacles. The accuracy of determining the coordinates in this case can fall to 20-30 meters, and sometimes more. Obstacles do not allow signals from some of the satellites that are potentially available at a given point on Earth. This leads to the fact that calculations are carried out on a smaller number of signals from satellites located mainly in one sector of the sky. An offset usually occurs in the perpendicular plane relative to the obstacle.

      In general, if we talk about the accuracy of GPS in the city, on the basis of the accumulated statistical data and personal experience, we can draw the following conclusions. The accuracy of determining the coordinates when the vehicle is in an open area (parking, square, etc.) and when driving on major highways, multi-lane roads will be 1-2 meters. When driving along narrow streets, especially when there are closely located houses along them, the accuracy will be 4-10 meters. When the car is in "yard wells", very close to high-rise buildings, etc. Accuracy can drop down to 20-30 meters.

      • The fact is that I have seen such information in some android applications, for example GpsStatus, and I do not understand how it is considered. My module works with GPS and GLONASS simultaneously. - Vladislav
      • @ Vladislav there probably implemented an adjustment using data from communication towers or wifi devices. Perhaps the information from this question is useful to you : .stackoverflow.com/ questions/ 143695 / … - Mstislav Pavlov