How does the TGP determine the location and distance to a target if it is obscured by clouds?

[RTS354]

I was using the TGP the other day while doing a SEAD  in a F-18. My technique is to place the TGP target box in the middle of the HARM box on the HUD, then I make the TGP SOI and select the target, and I also make a mark point. How does the TGP calculate the distance and location to the target if the target location is obscured by clouds? Lasers do not penetrate clouds so, this rules out laser range finding. Does the TGP use the F-18's ground radar to do this? Or, is the physics of the TGP not fully modelled in DCS when objects are obscured by clouds?

[Fresh]

Trigonometry.. it knows your position and attitude, it knows the terrain. Based on the angle down and in which direction it can calculate the position on the earth. It does the same even without clouds, (unless you use laser ranging). The further away the more inaccurate.. 

[RTS354]

That makes sense. Thanks for the info.

[Foka]

And also in DCS clouds does not block the laser. It's looong awaited and long time announced feature, still not implemented.

[graveyard4DCS]

21 hours ago, Fresh said:

Trigonometry.. it knows your position and attitude, it knows the terrain. Based on the angle down and in which direction it can calculate the position on the earth. It does the same even without clouds, (unless you use laser ranging). The further away the more inaccurate.. 

It could work, but I don't think there's a full elevation model in the Hornet's weapon system. This feature is available for more modern aircraft only. And there's a large error with such methods, making it unusable for GNSS weapon use.

It's only when there's a clear line of sight and the laser telemetry is working that you can get a good precision, even if that precision is in reality not always suitable for GNSS weapons use.

Also inaccuracy in linked to the angles: the closer you are to the vertical, the lower the uncertainty. And eventually, as it's derived from your own position, the precision of your navigation system matters a lot. 

Edited March 16 by graveyard4DCS

[Phantom711]

Am 16.3.2025 um 18:35 schrieb graveyard4DCS:

It could work, but I don't think there's a full elevation model in the Hornet's weapon system. This feature is available for more modern aircraft only

What? Where do you draw the line with regards to being modern enough for DTED? To me it doesn‘t sound like this could not have existed in the late 90s.

[Northstar98]

On 3/16/2025 at 5:35 PM, graveyard4DCS said:

This feature is available for more modern aircraft only.

Considering the Hornet we have is a TAWS-equipped aircraft (we have ground collision callouts representative of a TAWS aircraft and TAWS is an option present in HSI A/C page), ours is modern enough for DTED.

And DTED in general (or at least maybe a more rudimentary version) have been available since missiles using TERCOM have existed.

Edited March 17 by Northstar98

[AndyJWest]

According to a 2008 'official document' which I can't reproduce here, F/A 18s had DTED by then. It was integrated into both the HSI (as a grey-scale height map option), and into TAWS.

[graveyard4DCS]

You're totally right, TAWS relies on a DTED model.

My remark came from the fact that NASA's SRTM mission took place in 2000, and before that the elevation data was available mostly in "friendly" territories only. This was an issue because training with tools that you don't have in war time is "negative training". 

Also weapon systems were not as integrated as they are today, so having a DTED available for TAWS doesn't imply it's available for TGP trigonometry. I don't say it was the case, I just say it's not obvious. For example, the M2000D has a terrain elevation model, but it's only available for terrain following.

Anyways, it's an interesting question, I'll try to look if we can find docs about TGP's coordinates in the Hornet. 

[SOLIDKREATE]

If you look at "Angle of Centroid" and "Length of Leg"; you can use that part to calculate. I have a much newer version of this at work that I made. It has a few corrections. That part that I just talked about does work.

 

https://docs.google.com/spreadsheets/d/1fmdWWqcZ2Zwkc1U_SA7Zp94qTTkZCKLVkiXNooVyYmE/edit?usp=sharing

[Hulkbust44]

Combination of trigonometry, the DTED, and the radar if in the radar FOV. In DCS you can see that the radar is contibuting by RADAR or AGR on the HUD.


Sent from my iPad using Tapatalk

[Phantom711]

Am 18.3.2025 um 08:06 schrieb graveyard4DCS:

My remark came from the fact that NASA's SRTM mission took place in 2000, and before that the elevation data was available mostly in "friendly" territories only.

From what I just read on the internet, that mission was to provide DTED2 data. The less accurate DTED1 data already existed before. For what regions…I don‘t know. 
Then there is DTED0, which is basically a downscaled accuracy version of DTED1 in order to provide it free of charge to the public. This is also where some other (friendly) countries contributed data for. If this also means, that DTED1 only existed for „friendly“ territory, I don‘t know.

 

Edited March 20 by Phantom711