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Alternative GPS source (rpi)
http://forum.navit-project.org/viewtopic.php?f=12&t=642
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Author:  hackysack [ 23 Oct 2017, 12:27 ]
Post subject:  Alternative GPS source (rpi)

Hi,

This is a question about the daemon that serves up the GPS locations for navit (gpsd) and alternative GPS sources. If there is already a topic on this. Please point me in the right direction. Thanks.

I am building a recovery unit for 433 radios (tags). It operates offline. The unit is made up of a 433 IP router connected to a Pi via crossover. The pi is running a python handler that decodes that data and maintains staging files (latest record) for the different asset types.

Once a tag is seen (range from vehicle 2-4km), the unit automatically sends an activation command. If the tag has no GPS, the activation takes the form of an analog pulse on the same frequency (this provides direction finding location via NESDR). If the tag is fitted with with GPS (and has enough remaining battery), the GPS is activated for 1 hour.

The first version of the device used a GPS tag in the device itself, together with a received GPS location from a tag in the field. Using radian calculations and an onboard compass, the unit provides a relative bearing and distance from the finder.

The new version requires an offline map to plot any received locations. Ideally, to plot both the finder and the asset on the same map at the same time but I would be happy using the handler to switch between asset and finder when it is serving up locations for navit.

I have played with Tangram ES extensively but have been unable to combine my staging files with the geojson effectively. I won't say it can't be done but I couldn't.

Navit appears to be ideal. I have the uk OSM maps running happily. Centering/zooming config was easy.

The standard navit setup (on rpi3) uses gpsd daemon to interrogate the adafruit gps hat and serve up current locations. I would like to edit the local gps car profile source (source="gpsd://localhost" gpsd_query="w+xj") to do one of the following:
- point the navit.xml to a text file that contains a single (most recent) lat & long to plot
- create a new daemon that will serve up the lat&long in appropriate format

I would like any advice on how best to tackle a gps source that isn't a standard gps hat and the required input format for navit (what exactly does gpsd provide)?

If i can point the navit.xml to a text file, what format should the location be written in?

Is it possible to have 2 GPS sources to plot at the same time (eg"local gps car profile 2")?

Many thanks,
Ben.

Author:  KaZeR [ 27 Oct 2017, 19:43 ]
Post subject:  Re: Alternative GPS source (rpi)

Hi Hackysack, and welcome!

Quote:
Ideally, to plot both the finder and the asset on the same map

That's definitely possible within Navit. We used to have a feature allowing users to share their coordinates over udp. You could even set one friend as a destination and the route would update as the friend was moving.

Regarding the data sources, there's probably different way to tackle this.
One would be to used the 'pipe' vehicle. Most vehicles expect nmea compliant coordinates, but it would be easy to adapt that to a different format if you need to (although I would recommend making your data source nmea compliant as it would allow usage with many softwares).

How many assets do you need to track at the same time? If you need to track more than one, another possibility is to use the https://wiki.navit-project.org/index.php/Textfile or https://wiki.navit-project.org/index.php/Csv map sources which would allow you to track as many assets as you want at the same time. That map could be updated in real time via your existing finder.

Let us know if you have more questions!

We can also discuss that in real time via IRC : https://wiki.navit-project.org/index.php/Contacts#IRC

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