Author Topic: Incorrect GPS position sent to Trig TT22  (Read 3104 times)

DavidIOW

Incorrect GPS position sent to Trig TT22
« on: August 30, 2022, 10:34:28 pm »
I have PAW Rosetta set up to provide GPS input via NMEA to Trig TT22 for Mode S Extended Squitter (with SIL/SDA at 0 as required). I have followed all the set up advice and instructions in Trig and PAW ( baud rates etc etc) and there seems to be communication between the two devices communicating. However when I look at the gps position shown on the Trig (by double pushing the Trig Fn button) it shows a Lat/Long GPS position but it is just not very accurate! It puts us about 1.5miles south of where we actually are! More weirdly, PAW is also linked to Skydemon and on the SD map, when selecting ‘use PilotAware’ under the ‘Go Flying’ tab then it shows the plane in exactly the correct position (and I assume this GPS position is coming from PAW and not the iPad)! I have used the recommended USB to RS232 converter cable from Farnell so I am mystified as to why the Trig does not appear to be receiving the correct gps position and presumably will then also use that same, slightly incorrect, gps position when it transmits in ADS-B ES out? I have therefore not been able to use my transponder lest it is transmitting incorrect gps data. Any ideas of what I can check or fix? Is there a screen in PAW where I can read the gps position it thinks it is at? Many thanks!

Admin

Re: Incorrect GPS position sent to Trig TT22
« Reply #1 on: August 30, 2022, 11:01:25 pm »
Can I ask how you have determined the gps coordinates are incorrect?
Please explain your exact method
The reason I ask is whether you are using the correct coordinate representation

Thx
Lee

DavidIOW

Re: Incorrect GPS position sent to Trig TT22
« Reply #2 on: August 31, 2022, 10:26:33 pm »
Thank you for the reply, Lee. I have plotted the Lat/Long position read from the Trig on Google Maps, having converted the deg/min/sec format from Trig into degree decimals used by Google Maps. I checked the calculations so I think they are correct but I may be wrong. Here is the screen shot attached so maybe you can work out whether it is on the airfield or in the nearby town!? Hope it may be as simple as that!

Admin

Re: Incorrect GPS position sent to Trig TT22
« Reply #3 on: August 31, 2022, 11:10:15 pm »
Hi David

The same NMEA messages are sent to the trig, as are sent to SD
Also, you could download the track file to a wifi connected device and take a look at the NMEA messages which would go to the trig

Thx
Lee

grahambaker

Re: Incorrect GPS position sent to Trig TT22
« Reply #4 on: August 31, 2022, 11:59:23 pm »
Hi David.

If you create a user waypoint in SD using the coordinates as shown on the Trig display above, it is depicted as just outside the hangar at Sandown airport. Is that what you’d expect?

The Trig display is already in degrees and decimal minutes, and not deg/min/sec format, so doesn’t need converting.

DavidIOW

Re: Incorrect GPS position sent to Trig TT22
« Reply #5 on: September 01, 2022, 11:00:11 am »
Graham. I think you've spotted where I've gone wrong! If the Trig display is indeed in decimals, and not deg/min/sec as I had assumed, then the location you say you see on SD (outside the hanger) is spot on. I guess I should have noticed that the Trig was in decimals. Why do we have two (very similar) co-ordinate systems ...?   :-\ :-\

Admin

Re: Incorrect GPS position sent to Trig TT22
« Reply #6 on: September 01, 2022, 12:27:27 pm »
Graham. I think you've spotted where I've gone wrong! If the Trig display is indeed in decimals, and not deg/min/sec as I had assumed, then the location you say you see on SD (outside the hanger) is spot on. I guess I should have noticed that the Trig was in decimals. Why do we have two (very similar) co-ordinate systems ...?   :-\ :-\

Dont get me started on cartesian and polar co-ordinates as well ....

DavidIOW

Re: Incorrect GPS position sent to Trig TT22
« Reply #7 on: September 01, 2022, 02:36:38 pm »
Hmm. Still a bit confused here. I created that waypoint in SD using the text input format: N5038.9 W00111.1 and it puts it about 100m away. Is that the correct input format for SD for this co-ordinate? Really confusing these decimal degrees! Or is the ±100m a reasonable error?

AlanB

Re: Incorrect GPS position sent to Trig TT22
« Reply #8 on: September 01, 2022, 05:22:48 pm »
Hmm. Still a bit confused here. I created that waypoint in SD using the text input format: N5038.9 W00111.1 and it puts it about 100m away. Is that the correct input format for SD for this co-ordinate? Really confusing these decimal degrees! Or is the ±100m a reasonable error?

Have you tried

N50.389 and W001.111

A
Europa XS Mode-S ADS-B out enabled.

grahambaker

Re: Incorrect GPS position sent to Trig TT22
« Reply #9 on: September 01, 2022, 06:02:26 pm »
Hmm. Still a bit confused here. I created that waypoint in SD using the text input format: N5038.9 W00111.1 and it puts it about 100m away. Is that the correct input format for SD for this co-ordinate? Really confusing these decimal degrees! Or is the ±100m a reasonable error?
Don't input the coordinates using the wheels; touch the 'Touch here to type them in' and SD shows you the varios formats it will accept - the default one shown is the one you need - just type in the digits you see on the Trig display in the format SD defaults to.

DavidIOW

Re: Incorrect GPS position sent to Trig TT22
« Reply #10 on: September 06, 2022, 09:22:33 pm »
OK. Here is the latest situation...!

We met with Keith at LAA Popham who was extremely helpful (we had to drive there). Following his advice today we checked what the aircraft GPS position was from PAW linked to Skydemon. It was exactly correct on the SD map. We also looked at the co-ordinates of the aircraft that were showing at the top of our PAW traffic page. When these were plotted onto SD map as a user waypoint, again they were spot on. So it seems PAW has correct GPS position and is sending that correct position to SD. We then noticed that the co-ordinates showng on the Trig were still exactly the same as those in the photo sent earlier. However, since that photo had been taken we had moved the aircraft about 150m before we did the checks described earlier. It seems as if Trig has 'frozen' with a set of GPS co-ordinates that it picked up at some point from PAW and hasn't updated even as the aircraft has moved around. Any ideas? Thanks for all the input and guidance you've all given so far!

Deker

Re: Incorrect GPS position sent to Trig TT22
« Reply #11 on: September 06, 2022, 09:39:30 pm »
Our gps antenna gets covered when the canopy is slid back.
Is your GPS antenna in full view of the sky?


DavidIOW

Re: Incorrect GPS position sent to Trig TT22
« Reply #12 on: September 07, 2022, 09:49:05 am »
Yes. GPS aerial has a very clear view of the sky (and the GPS is the one attached to PAW which is giving the PAW the correct location when displayed on PAW or SD. It’s just the Trig that seems to be displaying the wrong coordinates even though they’re all using the same GPS input!

Deker

Re: Incorrect GPS position sent to Trig TT22
« Reply #13 on: September 07, 2022, 04:47:04 pm »
Yes. GPS aerial has a very clear view of the sky (and the GPS is the one attached to PAW which is giving the PAW the correct location when displayed on PAW or SD. It’s just the Trig that seems to be displaying the wrong coordinates even though they’re all using the same GPS input!

Email Trig,
I've found their tech support to be legendary.

Deker.

AlanG

Re: Incorrect GPS position sent to Trig TT22
« Reply #14 on: September 07, 2022, 04:48:21 pm »
Hi David I would first be inclined to pull the RS232 cable out of your PAW and this should then cause the Trig to not display a position as it will not have a feed.  If it continues to hold those co-ordinates then I would bve inclined to give Trig a call.  You should find them extremely helpful.  If it clears the co-ordinates then re-plug the RS232 and fire it all up and see what you get.

Regards
Alan