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How can I get the inaccuracy associated with the GPS data. For example when I read lat, lon, speed, heading data from a GPS receiver, how can I get an approximation on the inaccuracy that is associated with each of these data. For example the x position might be +-10m accurate or the speed might be +-3m/s accurate.

Can I obtain these inaccuracy from the GPS chip datasheet?

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Can I obtain these inaccuracy from the GPS chip datasheet?

No, because that's not a static thing – it depends on how many satellites your receiver receives at the moment, how strong the signals are, how long the receiver has been observing, at which temperature the receiver is operating, your speed, at which angles the satellites are, at which rate temperature is changing, your height, the availability of secondary info (like AGPS data), component aging...

Many GPS transmitters do emit standard format GPS messages, and these can (but not necessarily do, although it is a common feature) a positional variance estimate, which you can directly extract from these messages. Consult your GPS chipset's datasheet and any NMEA reference, if that's the format your GPS gives you.

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  • \$\begingroup\$ Thanks for the answer. I found this datasheet on the Internet and in Page 2 (specification), they have mentioned the accuracy for position, velocity and time. What are these inaccuracies then? sparkfun.com/datasheets/GPS/EM-406A_User_Manual.PDF \$\endgroup\$ – ManiAm Jul 16 '17 at 20:37
  • \$\begingroup\$ probably best-case lie-the-blue-from-the-sky specs? \$\endgroup\$ – Marcus Müller Jul 16 '17 at 20:47
  • \$\begingroup\$ I mean, it literally says "accuracy". Anyone who's selling a measurement system with a specified "accuracy" but not the statistical moments and the environmental conditions that were used to come up with that number is ... inaccurate, to say something relatively nice. \$\endgroup\$ – Marcus Müller Jul 16 '17 at 20:48
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To build upon Marcus Müller's answer, the GSA NMEA sentence can give you some information regarding the accuracy of a fix. You can typically get access to NMEA sentences with any given GPS chipset. It gives you number of satellites, whether the fix is 2D or 3D, and dilution of precision. You can analyze dilution of precision as a measure of accuracy of the fix in both horizontal and vertical components.

DOP (dilution of precision) is an indication of the effect of satellite geometry on the accuracy of the fix

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