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Reliable GNSS in urban cities

Application Notes November 28, 2014

You’ve bought the GNSS or GPS receiver, you’ve fitted it to your vehicle and you’ve driven to the city. But when you look at the results you know you are in trouble. Your customer isn’t going to accept them. What can you do to improve your GPS position?

This task is exactly what an Inertial+ is designed to do: improve positioning performance in cities.

OxTS has extended the range of GPS receivers that can be rescued from poor positioning with the addition of the NavCom SF-3050 receiver. The SF-3050 supports GPS and GLONASS for both L1 and L2 frequencies, so it is ideal for maximizing the performance in urban canyon conditions. The SF-3050 certainly showed itself to be very good at tracking both GPS and GLONASS satellites in urban conditions: making few mistakes and giving good coverage.

To show how good the Inertial+ and the SF-3050 are together we drove off to London on a route designed to upset even the most capable GNSS receiver. We looped round some back streets and down small alleys with high buildings on either side to make the task more difficult. We repeated our course 5 times so that we could show how repeatable the output was.

We were very pleased with the results. The SF-3050 doesn’t show drift at traffic lights, which other receivers we have tested are prone to do. It kept lock on a few satellites in the tightest urban conditions but successfully rejected satellites that were reflected off buildings, a common problem with receivers. The velocity measurements were accurate and didn’t push the Inertial+ off course.

The Inertial+ still made a significant improvement over the raw SF-3050 data, as shown in the figure below.

 

 

 

 

 

 

 

 

 

 

 

 

 

The blue line is the output of the Inertial+ whereas the purple line is the output of the SF-3050 by itself. The challenging environment can be seen in the Streetview image below.

600_iPlussf3050_ldn_street

 

 

 

 

 

 

 

 

 

 

 

 

 

The SF-3050 compared favourably to the Novatel OEM-V3 receiver that we also had in the vehicle. The Novatel receiver recovered much faster after going through a tunnel but the NavCom receiver gave better results in the dense urban conditions. In both cases the Inertial+ made a huge difference to the performance.

Copyright

The Google images in this document have been created from a licensed version of Google Earth Pro. Copyright of the images remains with Google.

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