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GPSD For Real Time Application

From: Kashyap Gada
Subject: GPSD For Real Time Application
Date: Sat, 28 Dec 2019 00:01:24 +0530

Dear Developers,

Firstly, appreciate all for this amazing project. Gratitude!!!

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.

Until Now -
Have built GPSD/CGPS/GPSMON from source on Raspberry Pi. Used UCentre to Fix 10Hz output from GPS. Tested a python and C++ source code. Tested them for more than 12 Hours continuous operation.

Next -
Developing stable client software that can handle 10hz update rates which can operate for 24x7 all round the year.

My Queries -
1. As per other posts on the mailing-list, 'gpsd accepts all what gps sends to it and forwards it even at higher frequency'. What does the gpsctl -c command which has minimum value of 0.25 actually do. Do its setting matter when GPS is sending data at 10hz or more? What cycle times mean in gpsd context.

2. For 100MPH and requirement of 5 meter accuracy what is ideal GPS frequency to be selected. I feel 10Hz is minimum that is required. But some where on the mailing-list i read replies where it was said that 1hz was more that enough in major applications and any speed more that that was not helpful. I didn't understand why higher rates are not required, even in such cases where there is high speed movement in vehicles.

3. I have set 10hz frequency in NEOM8U GPS through Ucenter and saved it in flash with a baud rate of 38400. The gpspipe log file 'gpspip-timestamp.log' is attached. Is this an optimum setting for my application? I don't mind occasional missing of locations btw.

4. Will python/c++ clients be able to receive or handle higher update rate outputs?

5. I have attached a python code I modified from a sample I found online. This code has a thread where next() is called with some sleep. And in the main loop i do some processing. This code, after operating satisfactorily for 5-6 hours, gives only one set of Lat/Long, even through cgps/gpsmon Lat/Long are changing. Read somewhere that you don't need to sleep in thread. I dont know what to do here. I need 10 hz latest location data in my python script how should i go about it. file name is ''

6. I need gps data only when the vehicle is moving above 10MPH. Is there any way to pause gpsd?

I haveĀ  tried to list all questions I had in my mind not to miss out any. Apologies for the long list.


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