TGP coordinates, what system provide them?

[falconzx]

During the previous patch i opened a bug report about the inconsistency of coordinates between INS(i guess) and TGP coord visualization. That topic has been merged with CZ problems, but i don't think this inconsistency has actually addressed as issue.
So, before opening a new bug report, i just wanna ask: which is the correct behaviour?

When i move TGP on the ground i see some coordinates, which is the system that is providing them? if it's the Nav system, why if i put a mark the coordinates appearing on DED are different from coordinates i see on TGP? And why if i make it steerpoint and i CZ i will never get again that point?

My guesses are that the nav system (INS+GPS) is constantly correcting, every frame. So when i move the TGP my alignment is different from the moment i create the mark. Is this the real airframe behaviour?

Edited January 26, 2023 by falconzx

[Sinclair_76]

Not 100% sure but...

Normally passive coordinate generation uses own position with azimuth/elevation of the line of sight from the TGP intersecting the DTED. 

But there's funky stuff happening with F-16 grid and the world grid. 

 

Edited January 27, 2023 by Sinclair_76

[silverdevil]

On 1/26/2023 at 1:07 PM, falconzx said:

During the previous patch i opened a bug report about the inconsistency of coordinates between INS(i guess) and TGP coord visualization. That topic has been merged with CZ problems, but i don't think this inconsistency has actually addressed as issue.
So, before opening a new bug report, i just wanna ask: which is the correct behaviour?

When i move TGP on the ground i see some coordinates, which is the system that is providing them? if it's the Nav system, why if i put a mark the coordinates appearing on DED are different from coordinates i see on TGP? And why if i make it steerpoint and i CZ i will never get again that point?

My guesses are that the nav system (INS+GPS) is constantly correcting, every frame. So when i move the TGP my alignment is different from the moment i create the mark. Is this the real airframe behaviour?

 

 

19 minutes ago, Sinclair_76 said:

Not 100% sure but...

Normally passive coordinate generation uses own position with azitmuth/elevation of the line of sight from the TGP intersecting the DTED. 

But there's funky stuff happening with F-16 grid and the world grid. 

 

 

another thing i have sometimes noticed is when lasing the same spot, more precise OR at least different.

[Machalot]

On 1/27/2023 at 1:20 PM, silverdevil said:

 

another thing i have sometimes noticed is when lasing the same spot, more precise OR at least different.

Lasing increases accuracy by providing a range measurement.

Are you entering the correct altitude when you type in the steerpoint coordinates? 

Instead of manually typing in the TGP coords on the DED, why not create a mark point directly from the TGP?

[d0ppler]

I have had problems with this before, but not in a very long time. Could you provide a short track illustrating your problem? It _can_ be an user error. But like Machalot is saying, if you're already using your TGP, just create a mark point directly. No need to enter those coordinates manually.

Bear in mind that there's always some slight inaccuracy when you slew your TGP to a steerpoint. That's at least what I'm experiencing when I "reset" the TGP position with TMS down. You'll get some slight deviation every time you TMS down. Don't know if that's what the real jet does, but the deviation is so small that it's not any problem.

[Sinclair_76]

6 hours ago, d0ppler said:

I have had problems with this before, but not in a very long time. Could you provide a short track illustrating your problem? It _can_ be an user error. But like Machalot is saying, if you're already using your TGP, just create a mark point directly. No need to enter those coordinates manually.

Bear in mind that there's always some slight inaccuracy when you slew your TGP to a steerpoint. That's at least what I'm experiencing when I "reset" the TGP position with TMS down. You'll get some slight deviation every time you TMS down. Don't know if that's what the real jet does, but the deviation is so small that it's not any problem.

The problem may seem small. However accuracy is such that a GBU-38 can’t be targeted effectively.

[falconzx]

Il 30/1/2023 at 05:50, Machalot ha scritto:

Lasing increases accuracy by providing a range measurement.

Yes that was true in the past. Now with the latest patch you don't have accuracy increases if you are aiming a point in the ground! Lasing allow you to update coordinates and elevation only if you are aiming to a building or on top of a vehicle. It's like TGP without laser "knows" the exact elevation of every point of the land mesh of the scenery without considering 3D object, but if you lase you can take in consideration the 3D object bounding boxes.

So what i noticed is: TGP coordinates display are the true coordinates of that land point, it's perfect, what is not perfect is our INS, so when you make a markpoint, the coordinates passed on DED are completely off! So if you want to save a precise coordinate of a point in a RECON activity, it's impossible through markpoints. You can only write down on paper what you read on tgp.

That's why i'm asking, what is supposed to be the origin of coordinates displayed by TGP? How can they be so perfect, and how the plane knows the exact point if the INS is so much inaccurate and instable?
 

Edited February 1, 2023 by falconzx

[dorianR666]

21 minutes ago, falconzx said:

How can they be so perfect, and how the plane knows the exact point if the INS is so much inaccurate and instable?

yes, its bugged.

the whole INS drift thing in dcs viper and hornet is WIP and full of issues. pretty sure the coordinates on tgp and in markpoint should be the same, because tgp calculates the coordinates from ins' ownship position and markpoint just saves the result from tgp.

[JTFF - Raph]

Hello,

Did you guys reported the bug and attached a track ?

If not we should do it to make sure ED team is aware of that problem (even if INS is in early access state)

Have a good day

[QuiGon]

On 2/1/2023 at 6:01 PM, falconzx said:

Yes that was true in the past. Now with the latest patch you don't have accuracy increases if you are aiming a point in the ground! Lasing allow you to update coordinates and elevation only if you are aiming to a building or on top of a vehicle. It's like TGP without laser "knows" the exact elevation of every point of the land mesh of the scenery without considering 3D object, but if you lase you can take in consideration the 3D object bounding boxes.

That is correct. It's called DTED: https://en.wikipedia.org/wiki/DTED

[QuiGon]

On 2/1/2023 at 6:01 PM, falconzx said:

So what i noticed is: TGP coordinates display are the true coordinates of that land point, it's perfect, what is not perfect is our INS, so when you make a markpoint, the coordinates passed on DED are completely off! So if you want to save a precise coordinate of a point in a RECON activity, it's impossible through markpoints. You can only write down on paper what you read on tgp.

Hmm, I tried to reproduce this, but in my test the TGP generated a MARK point that was exactly where I was pointing my TGP.
See attached track file.

Can you post a short track file of your own that shows this issue that you described?

Viper TGP MARK.trk

Edited February 12, 2023 by QuiGon

[falconzx]

I just replayed your track and I took a couple of screenshot from it to show what i mean

Here is when you just created the mark:
TGP shows 4150521 - 4147877
DED shows 4150527 - 4147882 

My question was: even if little, why this difference? which is the correct one? From where TGP take the datas if the DED shows another number? It's not a huge difference but is anyway more than .001

Here is after you recalled the steerpoint, so it's like asking our TGP: hey go on the coordinate stored, so i'm expecting it should be the second one, the one is showing on DED. And this is not happening, the TGP shows a new fresh coordinate.(in this case moved by the first one by .001 but this difference it's not constant if you do more tests)

TGP shows 4150520 4147876

DED shows 4150527 - 4147882 (the same as before)

Anyway the point you recalled is not anymore on the vehicle, but is on top of it. So this way of marking point is definitely unsuitable for precision bombing.

I'm not saying this is wrong, i'm just asking how it works, and if this is how it works in real Litening and Mark function.



 

Edited February 13, 2023 by falconzx

[BIGNEWY]

It has always been best to try and lock the base of the vehicle near the wheels for best accuracy 

[QuiGon]

54 minutes ago, falconzx said:

I just replayed your track and I took a couple of screenshot from it to show what i mean
 

Here is when you just created the mark:
TGP shows 4150521 - 4147877
DED shows 4150527 - 4147882 

My question was: even if little, why this difference? which is the correct one? From where TGP take the datas if the DED shows another number? It's not a huge difference but is anyway more than .001

Alright, I think I understand what you mean now. Based on your previous posts I was expecting a much more severe difference between TGP and DED coordinates as you said things like this:

On 2/1/2023 at 6:01 PM, falconzx said:

So what i noticed is: TGP coordinates display are the true coordinates of that land point, it's perfect, what is not perfect is our INS, so when you make a markpoint, the coordinates passed on DED are completely off! 

So after all they are not completely off, but actually very close together and differ just very slightly. I'm not saying this isn't an issue, just that I now understand what you were talking about and I gotta admit: I don't know where this difference comes from
It might warrant further investigation.

-------------------------------------------------------------------------------------------------
 

54 minutes ago, falconzx said:

Here is after you recalled the steerpoint, so it's like asking our TGP: hey go on the coordinate stored, so i'm expecting it should be the second one, the one is showing on DED. And this is not happening, the TGP shows a new fresh coordinate.(in this case moved by the first one by .001 but this difference it's not constant if you do more tests)

TGP shows 4150520 4147876

DED shows 4150527 - 4147882 (the same as before)

Anyway the point you recalled is not anymore on the vehicle, but is on top of it. So this way of marking point is definitely unsuitable for precision bombing.

This on the other hand is working correctly:
I was not using the laser when I marked the position on top of the vehicle. Because I was not lasing, the system did not take the roof of the vehicle as the position (as without laser it has no way of knowing the position of the vehicle roof or even just that there is a vehicle at all), but instead used its DTED data base to get the ground elevation at the position where the LOS of the TGP intercepts the ground. IMPORTANT: That happens BEHIND the vehicle as the vehicle is not known to the system, the LOS points right through the vehicle roof and intercepts the ground a few meters behind the vehicle.
Now, when I recall the MARK STPT (#26) and slew the TGP onto it, it points at that exact position, which is now seemingly behind the vehicle, because I haven't paused the game and was flying forward in the meantime and thus increasing the LOS angle from my aircraft to that position.
So there's no issue with this.

Edited February 13, 2023 by QuiGon