Quote:
Originally Posted by DaWei
It appears to be quite similar to the plotting we used to do in the olden days when I was a swabbie.
Since you have no radar, where are you getting the fixes which yield a track? How accurate and timely are they? I presume you're not on a moving platform, but wind could be a factor if the relative speeds are low.
Depending on the distances involved, you might be in a solid geometry situation, rather than a plane geometry situation. Figure all that out and apply your trig and you should have an interesting time.
I once made a dead-reckoning system for light aircraft. It was fun, but of course there was no market, since DME was being rapidly added to VORs (no GPS at that time, though).
Again, have fun, and don't hesitate to post your progress, or ask for help.
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Thanks again DaWei, don't worry, you'll all be hearing from me. You'll probably be sick of me.
In regards to your question about the tracks this is how it works.
As I said before aircraft are broken into categories. The first two categories are
IFR - Instrument Flight Rules. The aircraft fly on instruments basically.
VFR - Visual Flight Rules. The aircraft fly using visual reference to the ground.
IFR - An IFR aircraft will most often be using our VOR (VHF Omni Range) which is a navaid that transmits a signal and has 360 radials from it. This is how we get the track in this case. The pilot will report the radial from the VOR it is flying and it's distance using DME (distance measuring equipment). The VOR is located at the aerodrome, so the tower is pretty much the origin (I think that's what its called. Been a while away from geometry).
The are also lots of other VORs in other areas that the aircraft might be flying to, or they may be flying using GPS equipment. So the aircraft may not always be flying directly to the aerodrome. They may be overflying enroute to another location and cutting across the airspace (like a chord I think)
Once again its been a long time away from geometry. A simple description of a piece of controlled airspace can be discribed as a circle (on a 2 dimensional level) with the aerodrome in the centre.
Aircraft tracking by the "local" VOR follow a radius to the centre. Aircraft flying using a VOR from another location or GPS fly a chord. They will report where they came from and where they are going. The controller can then draw a line between these two locations and see their track.
VFR - They quite simply fly using topographical features. It may be a highway, a railway line, even electrical powerlines. The controller issues a clearance using specific locations within controlled airspace or the pilot flys a route that is already a published route and used all the time.
In all these cases thre controller will draw the track each aircraft will take, add "Tracking tolerances" and where the tracking tolerances overlap is where the aircraft enter conflict.
Tolerances are based on aircraft category (VFR or IFR), their altitude and in the case of IFR, tolerances vary depending on what sort of navigation aid they are using.
We also have a naviad called an NDB that isnt as accurate as a VOR so the tolerances for the NDB are larger.
VFR aircraft are tracking using topographical features, which I'm sure you agree is much less accurate that tracking by a navaid, therefore the tolerances are larger. The higher an aircraft is also has an effect. For example a VFR flying at 500ft over the top of a railway line would be much more accurate than an aircraft at 5000ft.
As for the size of the area involved. We are talking in the tens of nautical miles for a single location. In a perfect scenario where the aircraft is tracking to the local VOR and a VFR aircraft within controlled airspace you would need an area only about 20x20nm. In the case of an aircraft tracking GPS or between remote VORs in might push 50x50nm tops.
Note: I just re-read your post and noticed you are already familiar with the navaids. Sorry for explaining the obvious...
Also:
Wind: Not a factor. The tolerances have these sorts of factors already taken into consideration
How accurate: It is not a precise science. The controller uses a chinagraph and draws a pre-school like crayon line for the tracks and uses a ruler to draw up the tracks. The only accurate thing about it is the map it is drawn on. But we are talking distances in miles. The width of the lines would only represent a small fraction of the distances involved. If it is out by a couple hundred yards it doesn't matter. The program I make would have pin point accurancy though!