Fighter jet targeting computer coordinates

[user4455]

Does anyone know how the coordinates of a target and the plane are derived? And to what accuracy?

[Eddie]

How long is a piece of string?

 

This is an question that is impossible to answer. Every aircraft (even different models/variants/avionics suites/software releases of each aircraft) is different.

[marcos]

Knowing the position of the plane, the location of the pod, it's angle of rotation and the distance to the target, a series of transformation matrices can be used to produce a forward kinematic describing the location of the target. Differentiating that kinematic matrix will yield a Jacobian velocity matrix describing the speed of movement of the target relative to the aircraft, which can be inverted, potentially using Cholesky decomposition, to calculate how fast it must rotate in any given direction to maintain track of the target as the aircraft moves.

 

Also required is a means of target recognition which is usually achieved by contrast recognition to determine the edges of the shape

 

These kinematic matrix relationships are also used in robotics and computer graphics. Here's a book that I unfortunately had to read and understand in its entirety for my last job that explains how it all works including computer vision.

 

http://www.smpp.northwestern.edu/savedLiterature/Spong_Textbook.pdf

 

In most modern aircraft the position of the aircraft itself is determined primarily by GPS.

[user4455]

Perhaps I should have indicated I meant only stationary ground targets with relation to the plane, and not the workings of the plane's radar and computers.

 

You say GPS is used, and I might have guessed as much, but doing reading on the various ways a plane tries to prevent sending out signals from itself in order to remain silent in the air... I have no clue how such data transmission is effected.

 

I saw an interesting program on the military tv network, describing a new type of ground based heavy gun which shoots a large bullet designed to detonate at a given distance to the target, to either penetrate walls and explode inside a room, or to detonate in case of missing the target and prevent over-shooting.

 

The bullet knows when to trigger by rotating fast, somehow recognizing how many times it cuts through the earth's magnetic field gradient or whatever...

 

I was wondering if fighter jets could possibly use the same thing in any targeting, or something similar.... but probably not. I was wondering how the plane receives this information so that you could aim the HUD towards the known target, and in the distance have it locked automatically by the laser, and just fire off the missile.

[jazjar]

Well when you say to what accuracy, the MGRS coordinates go to 8 digits, which is a 10x10 meter box. This is only displayed to the pilot. Information for targeting the weapons systems is usually to a one by one meter box or smaller, which is necessary for GPS weapons targeting.

[EtherealN]

You say GPS is used, and I might have guessed as much, but doing reading on the various ways a plane tries to prevent sending out signals from itself in order to remain silent in the air... I have no clue how such data transmission is effected.

 

An aircraft does not have to transmit a single bit of information in any wavelength to get it's own position from GPS. All it needs to do is take in the signals from the satellites and do a little computing, just like your car GPS.

[jazjar]

Hmm, planes don't use GPS to navigate directly anymore. The A 10 uses an EGI system, which is an INS, a pimped out gyroscope, pretty much doing automatic dead reckoning for the pilot. Initial alignment data is provided by a GPS, and error correction is also provided by the GPS.

[SmokeyTheLung]

You say GPS is used, and I might have guessed as much, but doing reading on the various ways a plane tries to prevent sending out signals from itself in order to remain silent in the air... I have no clue how such data transmission is effected.

 

I'm not an expert, but I think GPS units basically receive signals from multiple satellites and use triangulation to produce coordinates. I don't think they send a signal to a satellite and receive coordinates in response.

 

The bullet knows when to trigger by rotating fast, somehow recognizing how many times it cuts through the earth's magnetic field gradient or whatever...

Interesting, I was under the impression that it was a bit more simple... The weapon has a way of determining accurate range to the target and as a round is chambered the fuse is programed depending on the desired result (basically a timed fuze, it's not difficult to chart out how long a specific round will take to get a certain distance) . That's how it works (?) with some newer Bofors cannons with programble fuzes I think

 

It sounded like Marcos explained it: But I'll give it a shot using some more approachable language :D

(The following is based on a limited understanding of how the a10 featured in DCS derives this info)

The jet uses GPS to get extremely accurate coordinates. The jet also has several senors to determine altitude (which AFAIK GPS isn't so great at). The plane also stores a 3d map of the ground (Digital Terrain System or DTS IIRC) it uses this to further refine its altitude measurements (its vital for the plane to know target altitude in addition to ownship altitude). Also, as Marcos pointed out, the plane/targeting pod is aware of the precise geometry of the cameras (same would be true of radars). After some fancy math, that would no doubt be impossible for with with a pen and paper, the plane can make some very accurate guesses about things like slant range and target coordinates.

I don't have any specific numbers on just how accurate these systems are but the USAF seems to be capable of dropping a JDAM within 9 feet of where it's intended. Close enough I think

 

EDIT: Chuck Norrised in the face three times over, dag :D I've got to watch for the roundhouse kicks

Edited September 8, 2012 by SmokeyTheLung

[aaron886]

Knowing the position of the plane, the location of the pod, it's angle of rotation and the distance to the target, a series of transformation matrices can be used to produce a forward kinematic describing the location of the target. Differentiating that kinematic matrix will yield a Jacobian velocity matrix describing the speed of movement of the target relative to the aircraft, which can be inverted, potentially using Cholesky decomposition, to calculate how fast it must rotate in any given direction to maintain track of the target as the aircraft moves.

 

Also required is a means of target recognition which is usually achieved by contrast recognition to determine the edges of the shape

 

These kinematic matrix relationships are also used in robotics and computer graphics. Here's a book that I unfortunately had to read and understand in its entirety for my last job that explains how it all works including computer vision.

 

http://www.smpp.northwestern.edu/savedLiterature/Spong_Textbook.pdf

 

In most modern aircraft the position of the aircraft itself is determined primarily by GPS.

 

 

This is how you get off, isn't it? :D

[user4455]

Seems to me if I want to fly a large distance and then easily lock my laser onto a target, then this is something that can't be promised in every situation.

 

Maybe later I'll post a more detailed question, but I can't dwell on this right now...

 

Thanks for the answers though.

[EtherealN]

Perhpas not promised with 100% accuracy every time, but if you have inertial systems, GPS updates for these, terrain data in place etcetera it actually becomes a (relatively) simple problem for the computer to figure out which direction to aim to place your laser right at the coordinate you gave it.