B4J Question Calculate Accuracy from NMEA-Sentence

D

Deleted member 103

Guest
Hi guys,

does anyone know how to calculate the accuracy of NMEA-Sentence?
In the $GPGGA sentence there is the variable "Horizontal Dilution of Precision (HDOP)", but that is not the accuracy.

$GPGGA,hhmmss.ss,llll.ll,a,yyyyy.yy,a,x,xx,x.x,x.x,M,x.x,M,x.x,xxxx*hh
1 = UTC of Position
2 = Latitude
3 = N or S
4 = Longitude
5 = E or W
6 = GPS quality indicator (0=invalid; 1=GPS fix; 2=Diff. GPS fix)
7 = Number of satellites in use [not those in view]
8 = Horizontal dilution of position
9 = Antenna altitude above/below mean sea level (geoid)
10 = Meters (Antenna height unit)
11 = Geoidal separation (Diff. between WGS-84 earth ellipsoid and
mean sea level. -=geoid is below WGS-84 ellipsoid)
12 = Meters (Units of geoidal separation)
13 = Age in seconds since last update from diff. reference station
14 = Diff. reference station ID#
15 = Checksum
 

drgottjr

Well-Known Member
Licensed User
Longtime User
i was hoping that link would deter you 😷
 
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Bracket

New Member
that's why I asked the question here, with the hope that someone would have an easier solution. ;)
Hi Filippo,
The NMEA sentence actually containing accuracy (in meters) for the position-solution is called GST.

i.e.:
$GPGST,143333.00,7.38,1.49,1.30,68.1409,1.47,1.33,2.07*4A

(don´t get messed with "7.38,1.49,1.30,68.1409" they are related with other statistic concepts/nuances).
You can use the following as very reliable estimators of the "position-solution" error I suspect you are looking for:
1.47 --> "estimated" error (in meters) in Latitude.
1.33 --> "estimated" error (in meters) in Longitude.
2.07 --> "estimated" error (in meters) in Altitude.

(I quote estimated because there are lots of statistic concepts and calculations involved and hence some scholars could add lots of comments).
(PDOP, HDOP, GDOP, etc. contain "relative" values hardly translatable to meter values).
I hope this helped.
 
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