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Satellite Pseudoranges

asked 2014-08-11 09:27:22 -0600

Naz gravatar image

I am trying to retrieve the Pseudoranges from the satellite to the GPS receiver mounted on the Husky robot. The type of messages I have related to GPS are :

sensor_msgs/NavSatFix

nmea_msgs/Sentence

sensor_msgs/TimeReference

geometry_msgs/TwistedStamped

geometry_msgs/PoseWithCovarianceStamped

All I can log now is GPS solution (longitude, latitude and altitude) which is part of the sensor_msgs/NavSatFix message . I wonder where can I find the Pseudoranges from the satellite to the GPS receiver.

Thanks in Advance,

Naz

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The default ROS driver probably doesn't expose the data you're looking for. You should probably contact Clearpath or the GPS manufacturer directly.

ahendrix gravatar image ahendrix  ( 2014-08-11 14:30:10 -0600 )edit

Can you tell us what you're trying to do with the pseudoranges?

Tom Moore gravatar image Tom Moore  ( 2014-08-12 13:30:13 -0600 )edit

Sure, I am trying to estimate the relative distances between two vehicles. The two vehicles are equipped with GPS , using the Pseudoranges and the satellite positions the relative distance can be computed using the double differencing method.

Naz gravatar image Naz  ( 2014-08-12 13:40:33 -0600 )edit

Here is a link to the GPS integrated in our Husky robot (vehicle) : http://static.garmincdn.com/pumac/GPS...

Naz gravatar image Naz  ( 2014-08-12 13:41:15 -0600 )edit

A quick read of the datasheet suggests that your GPS doesn't provide pseudorange output.

ahendrix gravatar image ahendrix  ( 2014-08-12 20:10:34 -0600 )edit

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answered 2014-08-12 13:46:34 -0600

Tom Moore gravatar image

There are other methods for calculating the relative distance between two lat/lon coordinates that don't require knowledge of the individual pseudoranges to satellites. Also, if you use the utm_odometry_node in the gps_common package, you'll get UTM coordinates for each of your GPS positions. The UTM coordinates are given in meters, so computing the distance between two of them should be trivial. Are those methods insufficient for your needs?

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I am specifically working on enhancing the algorithm of double differencing using Kalman filter by figuring out the errors in Pseudoranges due to multipath and depending also on the carrier-noise-ratio of the pseudorange received.My main research is about relative distance using double differencing.

Naz gravatar image Naz  ( 2014-08-12 13:53:27 -0600 )edit
1

Gotcha. Offhand, I don't know of any existing ROS nodes that extract that information from GPS units. You might want to go the route suggested by @ahendrix. Alternatively, if the 18x provides that information, you can create or modify the existing ROS packages to produce the data you need.

Tom Moore gravatar image Tom Moore  ( 2014-08-12 14:08:05 -0600 )edit

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Asked: 2014-08-11 09:27:22 -0600

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Last updated: Aug 12 '14