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MLAT flag - basestation

Posted: Tue Aug 18, 2015 3:13 pm
by ProHill
Hi Andrew,

I see that the latest preview includes a flag to show whether an aircraft's position is from MLAT, which is very cool. Does this flag flow into Basestation.sqb by any chance? If not, that would be of definite interest.

One other thing: it appears that MLAT aircraft do not get their basestation db FirstLat/FirstLon/LastLat/LatLon updated. Is this possible?

Thanks!

Andy

Re: MLAT flag - basestation

Posted: Wed Aug 19, 2015 3:35 pm
by agw
Unfortunately there's no field in BaseStation.sqb to record the IsMlat flag, so no. Perhaps when I finally get around to the full-track database, which won't have to follow Kinetic's schema, I'll be able to record things like that in there.

MLAT positions and the database writer - are you recording a merged feed that has MLAT positions on it? The intention is that if you want MLAT positions recorded then you'll need to record the merged feed and not one of the constituent feeds. However I can imagine how the recent MLAT changes might stop this from working properly, I'll take a look.

Re: MLAT flag - basestation

Posted: Wed Aug 19, 2015 4:03 pm
by agw
I've had a look at the code and I think it should work if you have the database writer record the merged feed. However there are some things on the MLAT feed that should be ignored if there is a better source, e.g. the altitude, so I'll be addressing that in the next preview.

Re: MLAT flag - basestation

Posted: Wed Aug 19, 2015 9:45 pm
by ProHill
Thanks for the info - too bad on the schema. That second point was my bad - I forgot about the feed being selectable in the database writer. It does work now. :)

Re: MLAT flag - basestation

Posted: Sat Aug 22, 2015 8:51 am
by Martin
This MLAT flag behaves strangely. With an aircraft at the limit of my range, the flag keeps swapping between Yes and No. When the Receiver is my Beast the flag is Yes, when the Receiver is MLAT the flag is No. This is not what I would have expected.

Re: MLAT flag - basestation

Posted: Sun Aug 23, 2015 7:38 pm
by agw
When the receiver is the Beast there are no position messages, so they're being set by the MLAT feed - hence the MLAT value of YES. It means the positions are coming from MLAT.

When the receiver is the MLAT receiver there are position messages on the feed for the aircraft and they are indistinguishable from a transmitted position message, so VRS sets the MLAT flag to NO. The positions were transmitted (as far as VRS was concerned) and they are not coming from MLAT.

Ticking the MLAT box for a merged feed does not mean "Everything on this feed is a position message that has been calculated by an MLAT server somewhere". You could have a mix of calculated and transmitted positions, e.g. that feed might be a merged feed. That MLAT box just says "If there is a position for an aircraft on here, and it looks like the nominated receiver for this aircraft isn't getting position messages, then you can use the position messages from this feed".

Some MLAT software will put a marker on the message to say that it's a calculated position instead of a transmitted position. If your software is doing that then VRS will detect it and will show a YES for MLAT even when the receiver is the MLAT feed. It will be permanently set to YES for the aircraft regardless of which receiver is in use.

Re: MLAT flag - basestation

Posted: Sun Aug 23, 2015 9:27 pm
by Martin
Thank you for the explanation, all understood. I am using mlat-client.exe so, what I need is for that program to mark messages as calculated then the MLAT flag will remain set to Yes.