Can I use NMEA data to generate a GPS signal on the fly using the GPS Simulation Toolkit?

[TimothyWright]

I am wanting to generate a GPS signal to simulate driving along a given route.

Already, I have NMEA 0183 data for the route I am trying to simulate and I basically want to play it back.

How can this be done with the GPS Simulation Toolkit?

Thanks!

[mikealder]

What device/ software are you trying to display the route on, if its a PDA or PC based package have you looked at Fransons GPS Gate as that offers a cheap way to replay stored NMEA data - Mike

[TimothyWright]

I'm actually trying to see the route on a portable navigation system (Nuvi, TomTom). I want to to use the GPS Simulation toolkit to transmit the satellite signal and have it follow a route I know. The toolkit documentation says it can do on the fly movement, but the example only shows ECEF (XYZ) input not latitude longitude input.

[Jim_S]

Hello Timothy,

You are correct that the GPS Simulation Toolkit can transmit the signal and have the navigation device follow the route. The example I would start with is the niGPS Direct Streaming Generation with on the fly parameters. This example, like you mentioned use ECEF instead of LLA receiver location format. You can change this by modified the first property node. Instead of using Initial X, Y, Z, you use Degrees, minutes, Seconds and direction for both latitude and longitude. Along with making this change, you will need to add the property of Receiver Location Format before these to ensure that this executes first.

After this, I assume that you would want the receiver velocity format in a different format than ECEF. Like the Receive Location Format, you will need to change to the appropiate format and the appropiate initial values.

[TimothyWright]

I did try to just change the ECEF to LLA and use the Initial Lat/Long Degrees/Minutes/Sec, but I saw this in the documentation for the EnQueue Motion parameters VI:

"niGPS Enqueue Motion Parameters

Enqueues the Initial X, Initial Y, Initial Z, and Trajectory Simple Travel Time properties when the Trajectory Mode property is set to Simple.

This VI enqueues the Trajectory Script String property value when the Trajectory Mode property is set to Script. If you set the Receiver Location Format property to LLA, the toolkit sets this property value to ECEF format and enqueues the property.

Note Call the niGPS Enqueue Motion Parameters VI to enable and use the On the Fly Input Mode. "

You also get the following error if you try to change the receiver format while the data is being generated:

"Error -20442 occurred at gpsv2_validate state.vi

Possible reason(s):

All the attributes except Relative Power (dB), Channel Disabled?, and Disable SV User Scaling, cannot be set on the fly."

Looks like it only supports ECEF.... Would be nice if there were a VI to convert from LLA to ECEF, but I do not see that either.

[Jim_S]

Hello Tim,

I ran a test with that example today to valid the error and I didn't receive an error. By the looks of the information it provides, you are changing the Relative Power (dB), Channel Disabled?, or Disable SV User Scaling which can't be set on the fly. Are you changing these values?

It does look like this isn't possible with GPS. I must have missed that in the help. Sorry for the confusion.

[TimothyWright]

I'm not making any changes to the 3 settings in the error message. In fact if you look closely at the error it seems to indicate that these 3 parameters are the only ones you can change.

If I only change Lat/Long Degrees/Minutes/Seconds properties, I do not get the error message, but when the Enqueue Motion vi is called it automatically changes the location format property from LLA to ECEF, essentially disabling any code that would use the Deg/Min/Sec properties, I assume.

The reason I get the error, is because I try to set the Trajectory Location Format property back to LLA, which is apparently not allowed.

I did find a couple of subVIs that get installed with the GPS toolkit "gpsv2_update properties LLA to ECEF.vi" and "gpsv2_update initial properties LLA to ECEF". I am going to try some stuff with these VIs. Hopefully, they will do what I need.