HDOP and VDOP in mavros?

[itzmejawad]

Hi.. is there any way to request HDOP and VDOP data

Subscribing to /mavros/global_position/raw/satellites , it gives only the number of satellites..

and also if i subscribe to /mavros/global_position/raw/fix, it gives

but how can i get the position accuracy value, hdop and vdop? is there any topic for that?

Otherwise what is this position co variance... what is the safe threshold for that?

Mavros: ?0.18.4? ROS: ?Kinetic? Ubuntu: ?18.04?

[ x ] ArduPilot [ x ] PX4

[vooon]

position_covariance.

[Harishferose]

@vooon

I am new to mavros, I need HDOP and VDOP Values

Cant able to understand the position_covariance matrix

Can you share how to fetch/calculate the HDOP and VDOP Values from position_covariance

Thanks in advance

[vooon]

https://github.com/mavlink/mavros/blob/c121f6bde0b47bc031bf92a9a746bac4970944c7/mavros/src/plugins/global_position.cpp#L180-L193

[selvanathans]

@vooon Could you share this snippet as python?

[vooon]

That's just a code that computes covariance in the plugin. You can extract eph/epv or h/v accuracy doing opposite. I.e.:

1. if type==1: eph, epv = sqrt(cov[0,0]), sqrt(cov[2,2]) (NOTE: eph/v are unitless)
2. if type==2: h_acc, v_acc = sqrt(cov[0,0]), sqrt(cov[2,2]) (NOTE: h/v acc are in meters)

[itzmejawad]

@vooon Thank You :)