Primarily for general aviation discussion, but other aviation topics are also welcome.
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#1699227
@Cub
As you have raised the question of the purpose of NACp - or a containment area by any other name, a simple question for you, as SkyDemon is the consumer of the GDL90 data in question (or any other EFB in fact) - what do you suggest SD should do when receiving a GDL90 traffic report with a given NACp from the possible legal set of values of 0 - 11 ?

Use the value accordingly - if so how ?
Ignore the value completely ?

I am happy to provide data in a different format, and I think that is the way forward, so in this - we are in agreement.

For the purpose of clarification, how do you think NACp should be utilised in its current form in an EFB ?

Thx
Lee
User avatar
By Cub
#1699235
PaulSS wrote:@Cub
Or maybe you are not bothered?


Why would you even bother writing such a stupid thing when you know full well he's 'bothered' and is trying to produce the best data possible?

Perhaps if you came up with something more than 'unable' when requested for your data things might progress. It's incredibly easy to sling s*#t from the sidelines but it takes a lot more to actually do something to help and all I've seen you do is criticise and put up roadblocks :roll:


It was a genuine challenge Paul. PAW may not be worried about how third party apps receive and process their data. After all, PAW has it’s own proprietary display and alerting functionality which presumably 3000+ users are perfectly happy with?

You will probably never know how helpful or unhelpful I have been to this debate or the rollout of EC in general. Anyway, on this rather sour note I will bow out gracefully, not because of a timely flounce but because after nearly 39 years I am leaving air traffic control and in a few days time, taking up a role which unfortunately (for me at least) means it will be inappropriate for me to comment in this area.

I think, I look forward to working closely with some of you in the future ;-)
flybymike, gaznav liked this
#1699246
leemoore1966 wrote:For the purpose of clarification, how do you think NACp should be utilised in its current form in an EFB ?


The GDL90 Spec makes a recommendation there:

MFD Recommendation: Targets with either a NIC or NACp value that is 4 or lower (HPL >= 1.0 NM, or HFOM >= 0.5 NM) should be depicted using an icon that denotes a degraded target.

It also has a specific field for Address Type which precedes the 24-bit Participant Address:

t = 0 : ADS-B with ICAO address
t = 1 : ADS-B with Self-assigned address
t = 2 : TIS-B with ICAO address
t = 3 : TIS-B with track file ID.
t = 4 : Surface Vehicle
t = 5 : Ground Station Beacon
t = 6-15 : reserved


It strikes me that you could use that to identify MLAT derived positions -- after all it's pretty much TIS-B. But perhaps you've already discussed that with Tim.
#1699247
PaulSS wrote:@Cub
Or maybe you are not bothered?


Why would you even bother writing such a stupid thing when you know full well he's 'bothered' and is trying to produce the best data possible?

Perhaps if you came up with something more than 'unable' when requested for your data things might progress. It's incredibly easy to sling s*#t from the sidelines but it takes a lot more to actually do something to help and all I've seen you do is criticise and put up roadblocks :roll:


I had similar thoughts about Cub's post :-( It was good but the good was undone at the end.
Stu B liked this
User avatar
By mo0g
#1699261
Cub wrote:Anyway, on this rather sour note I will bow out gracefully, not because of a timely flounce but because after nearly 39 years I am leaving air traffic control and in a few days time, taking up a role which unfortunately (for me at least) means it will be inappropriate for me to comment in this area.


I sincerely hope that this is not with SkyEcho, or any other competitor to PAW, because if so everyone should re-read your posts on this thread with a big red flag waving about?
#1699270
bookworm wrote:
leemoore1966 wrote:For the purpose of clarification, how do you think NACp should be utilised in its current form in an EFB ?


The GDL90 Spec makes a recommendation there:

MFD Recommendation: Targets with either a NIC or NACp value that is 4 or lower (HPL >= 1.0 NM, or HFOM >= 0.5 NM) should be depicted using an icon that denotes a degraded target.

Hi Bookworm
This is the crux of my question that I was trying to get @Cub to comment.
What should the EFB do in this case of NACp lower than 4 ?

@Tim Dawson kindly modified SkyDemon to show degraded targets using the ambiguity circles (which we emulated for MLAT), and this led to the situation that lots of ADS-B emitters started showing up as degraded targets, as their NACp was such.
I think this resulted in Tim receiving complaints from users that all of these aircraft had huge ambiguity circles.

I agree with cub we should not 'bastardise' GDL90, so lets generate the ambiguity for MLAT using a different method, agreed

That leaves the elephant in the room which is - what is the point of the ADS-B emitter calculating a NACp, if it is going to be ignored because you don't like what it tells you ?

Thx
Lee
#1699286
I think NACp would have been useful and that’s why I (temporarily) implemented ambiguity circles for our map display. It’s just unfortunate that some devices output rubbish for that field. It makes it unusable, by anyone, for any useful purpose. Such is life sometimes when it comes to protocols :(
leemoore1966, gaznav liked this
#1699304
That leaves the elephant in the room which is - what is the point of the ADS-B emitter calculating a NACp, if it is going to be ignored because you don't like what it tells you ?


We discussed this ad nauseam here: viewtopic.php?p=1664093#p1664093

I (think) the long and the short of that discussion is that there are some odd combinations out their in “SIL=0 land” that are giving out some low NACp that generate mahoosive circles. Please, let’s not go back to this again just because one EC user wants to implement it for their own gains - thanks. :thumright:

Image
Flyin'Dutch' liked this
#1699324
Cub wrote:<snip>…after nearly 39 years I am leaving air traffic control and in a few days time, taking up a role which unfortunately (for me at least) means it will be inappropriate for me to comment in this area.

I think, I look forward to working closely with some of you in the future ;-)


Good luck in your new role :thumleft:
PaulB, kanga liked this
#1699329
It seems to me that there is a great deal of good work going on to try and provide well qualified EC data and @leemoore1966 in particular is pushing the boundaries of what's practical. Others appear to have determined to sit in a clearly defined niche and that's fine too.

@Tim Dawson is right in my view to challenge proposals and seek to ensure that what we see and hear is well understood by us less sophisticated pilots.

Which product one chooses will be determined by style of flying, price and functionality and it's good to have some choice even though it may be a bit limited at this point.

Some on this thread would do well to note that we're not looking at right and wrong but considering possibilities and differences in a field where the developers are essentially pioneers, with all the risk and uncertainty that brings. Encouragement, gratitude and positive critical assessment are suitable responses to my mind.
patowalker, derekf, Tim Dawson and 11 others liked this
#1699398
On the NACp value, see this paper for some more background: https://www.sciencedirect.com/science/a ... 610860120X . See table 1 where it says what is recommended for each NACp level.
I still don't see why it shouldn't be used for MLAT as it simply specifies that the device thinks there is a 95% chance that it within the defined radius (based on some maths) although I don't think I've seen the actual GDL90 specification online anywhere in detail (does it specify how that field should be calculated?) so is this really bastardising a field?
I struggle to see the difference to an end user, whether a decide is unsure of its position or MLAT is unsure of its position. A GPS device will very quickly become unsure of its position if you do aeros.

Perhaps everyone would be happy if the recommendations that are referenced in that paper, in what do with with certain NCAp levels, are adhered to?
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