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Re: [External] Re: GPSD For Real Time Application

From: Joshua Quesenberry
Subject: Re: [External] Re: GPSD For Real Time Application
Date: Mon, 30 Dec 2019 11:38:46 -0500

It looks like the NEO-M8U does an Untethered Dead Reckoning relying only on its own internal sensors (claiming no need for wheel tick sensors) and GNSS making this a rather neat little device. UDR combined with an output rate of 30 Hz (1.49 m / update) seems like this might work for your application. You'll definitely want to increase the UART bitrate (460800 looks like the highest supported) or maybe even switch over to the USB interface that it has available. You likely also want to put the device into binary mode rather than using NMEA strings. I've not used GPSd in binary mode, but my understanding is that it should support UBX binary, hopefully it can perform well at 30 Hz otherwise you may need to read/decode the data directly in your application. SBAS will be important if you don't have any other form of corrections coming in. If you need a better positional accuracy you're likely looking at needing a more expensive GPS/INS setup. Novatel makes some solutions that I've been around, they have an expensive satellite-based subscription that's a couple grand per year that can get the GPS error well below 1 meter and an add-on IMU to help with dead-reckoning, but all of this together is probably $10-20k.

On Mon, Dec 30, 2019 at 9:17 AM Kashyap Gada <address@hidden> wrote:
Hi John,

The Ublox GPS ( already come with IMU within them and with data rates upto 30Hz. Do we still require post processing?


On Mon, Dec 30, 2019 at 7:32 PM Burton, John <address@hidden> wrote:
A UBLOX GPS receiver is fine for stationary and relatively slow movement. If you are looking for accurate positioning at higher velocities you will need to add IMU/INS (motion sensors) to the mix. Even cell phones have motion sensors that help Google Maps keep track of where you are.

Many commercial grade drones / UAVs have GPS-aided INS systems that do exactly what you are trying to do:

If you want to combine the GPS+IMU data yourself, or if you just what to use GPS in a higher speed application, you should probably use some sort of filtering (Kalman is the defacto standard) to smooth out the measurement noise / uncertainty so that your location and motion data will actually mean something and not just be noise. One example of this is:

On Sun, Dec 29, 2019 at 10:49 AM Kashyap Gada <address@hidden> wrote:
Dear Bernd,

How can we mix gyro data with GPS to get better location?
Vehicle Locomotive, Can get wheel tick.
What can additional sensors be?


On Sun, Dec 29, 2019 at 9:11 PM Bernd Zeimetz <address@hidden> wrote:

On 12/27/19 7:31 PM, Kashyap Gada wrote:
> My application -
> Record some events/sensor readings in a moving vehicle 100MPH using a
> Ublox Neo-M8U GPS. Accuracy required is better that 5 meters.

additionally to the comments you've got so far:
I think you should at least have an additional gyro sensor which gives
you some movement data to combine with what you've got from the GPS.
Also if you have other sensors in your vehicle - use them.
You did not mention which kind of vehicle and what you are doing with it
- but if you are not 100% sure that you'll always have good gps
reception (or that you are not close to chinese pig farms with fake gps
transmitters), you *will* have to use additional sensors.

 Bernd Zeimetz                            Debian GNU/Linux Developer                      
 GPG Fingerprint: ECA1 E3F2 8E11 2432 D485  DD95 EB36 171A 6FF9 435F


John Burton, Ph.D.
MTEQ, Inc.

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