Forum: General Topics

Hi Stephen,

Just wondered if you could explain exactly what the satellite screen shows?
I'm guessing that the circles are the position of satellites overhead (as if you were looking straight up at the sky?)
The barchart underneath is the signal strengths?
The numbers, are these just arbitary numbers to tie the positions with the signal strength, or are they actual serial numbers coming from the satellites?
The circles also seem to change colour (shades of green)
Anthing else of interest?
I know none of that information is of any real use, but it would be interesting to know what it all meant...! :-)

Hi!

Interesting to hear. A few other questions! :-)

-I have occassionally noticed that there are straight dotted lines from the currently activated satellites converging at another satellite. Is this to indicate that the reciever currently has a DGPS/EGNOS fix?

-Does TMJ decide wich satellites are beeing used to determine location and recieve DGPS-corrections, or is this done by the receiver?

-What does the small flashing red dot in the lower right corner and the very small red dot moving in the bottom of the gauges screen indicate?

As I have said before, very nice application. Like it a lot!

Regards
Jonte

Hi Jonte,

Its actually not as clever as all that! The dotted lines you are seeing are sort of a bug I suppose. They are part of the trace of the satellites paths as they move across the sky. When TMJ first connects to the GPS device it immediately uses the satellite positions reported by the GPS as the 'starting' point for showing their location history. However, if at that point the GPS hasn't achieved a fix at all (ie if it has just been switched on after a long period of inactivity), then it is likely to list all the satellites as being in the same place (most like zero azimuth and zero altitude). When it does subsequently get a fix the satellites positions will suddenly jump to their correct positions, giving the effect that they have all come from a single point.

TMJ has no control over the GPS device whatsoever, it simply reads the stream of NMEA Sentences which the device generates, which give the lat/long/alt/time/date/etc information, plus a bit of info about the satellites positions/signal strengths. Some good info on NMEA sentences here.

The two dots are mainly for testing/debugging purposes. The bottom-right one flashes each time a valid GPS signal has been received from the GPS device, whilst the scrolly one along the bottom moves one pixel to the right each time the screen is redrawn, so the faster it moves the more 'frames per second' are being displayed. TMJ only tries to update the screen once per second though, so this is pretty useless - its just there because I forgot to remove it!!

Cheers,
Stephen