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DPChallenge Forums >> Photography Discussion >> foreshortening or near death experience?
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01/29/2006 03:52:53 PM · #1
I know men are prone to overestimating small distances, but 2.5 miles???!!

I don't believe the jets are of sufficiently different sizes to explain this, but please someone persuade me otherwise...
01/29/2006 04:03:52 PM · #2
I agree .... I can not believe 2.5 miles, either (and I am pretty darn good at judging distances *s*).
01/29/2006 04:06:33 PM · #3
The two aircraft involved are of vastly different sizes, the further of them being much larger. That certainly helps create the (deceptive?) appearance of being so close. I'm not certain if the picture is real or not, or how far away they are, but I've been involved in aviaton for a long time, and would be surprised if they really were that close.
01/29/2006 04:08:40 PM · #4
looks like 2.4 miles to me, personally.
01/29/2006 04:08:41 PM · #5
If you take into account the possible vertical and horizontal distances that could produce this image (left hand plane 1000's of feet lower and horizontally displaced by 1000's of feet) 2.5 miles doesn't seem that unreasonable.

The difference in distance between the aircraft and the photographer can account for the apparent similar sizes, I'd suggest.

01/29/2006 04:22:37 PM · #6
I dunno, this picture looks like it was taken from nearly straight below... so to get that forced overlapping perspective, most of that 2.5 miles distance would have to be vertical, wouldn't it? even at a 30 degree angle, that would mean one plane was something like 1.75 miles above the other...

whatever, it looks fishy but ultimately makes no difference, and if the Brits were unconcerned, I will be too.

perhaps I shall go play a certain Online Tennis Game
01/29/2006 04:29:48 PM · #7
The spokesman said there was no question that either aircraft had strayed from its proper path, which should mean there was a distance of some two and a half miles between them.

I think you are misinterpreting...the statement says they SHOULD be that far away from each other, not that they ARE that far away from each other. If they stayed on their proper path they should be 2.5 miles apart but obviously one or both strayed from its flight path.

Message edited by author 2006-01-29 16:30:25.
01/29/2006 04:31:35 PM · #8
It wouldn't be difficult to get a rough idea. If someone could identify the types of planes they were and look at their length, a ratio should be fairly easily derived which would at least give you an idea if they planes were close or not.

You couldn't tell any distances though as we don't know how far away the photographer was.
01/29/2006 04:32:29 PM · #9
This image is a bit odd, but I also find the range variance difficult to believe. If the JAL is a 777-200 then it is about 209 feet or 64 metres in length. Whereas, if the DHL is a 737, then it is about 102 feet or 31 metres in length. This is a 2:1 ratio in size. But, that does not seem to calculate to validate this image.

If the two aircraft where departing from parallel runways and one (DHL) was crossing under the other (JAL), then there is a horizontal and a vertical separation to consider. So, it might be true, but I would love to see the math before I am convinced. We would need to know the altitudes of each aircraft and the size of the original image.

The DHL looks like it is in the process of cleaning up for flight - ie: retracting its gear and flaps, whereas the JAL is already clean. This suggests that the JAL is further from the end of its runway than the DHL. Therefore, the JAL would be at a greater altitude, which is evidence in the photograph. It is likely an issue of perspective and not a near miss in my opinion.

Fun stuff, just the same.

Message edited by author 2006-01-29 16:39:18.
01/29/2006 04:42:17 PM · #10
Originally posted by mycelium:

I dunno, this picture looks like it was taken from nearly straight below...


Could they both be a in a left bank turn? That would show more of the underside without the need to be 'below' them.
01/29/2006 04:46:41 PM · #11
My point exactly Morgan. If those planes are as you said (I didn't noticed if they were identified), then their ratio of lengths should be 2.06. The more divergent the ratio we see, the further they are apart. By measure, their ratio appears to be 1.31. In other words, the larger plane "appears" to be over 50% too small.
01/29/2006 04:50:09 PM · #12
i think this is awesome photo :-)
01/29/2006 05:09:55 PM · #13
When they're talking about ".. all sorts of systems going off ..." they're talking about an on-board gizzmo called TCAS "Traffic Collision Avoidance System" as well as Air Traffic Control's digital radar systems. Both are mandatory in Euro Airspace.

Both are calibrated to wake the dead if separation is compromised. These days there's no way a pilot can have an Ooops without Big Brother knowing about it. I think they're simplifying their explanation a little for public consumption here. The 2.5 mile statement is not about the vertical sparation we're seeing here, but about separation at the same altitude. From memory, the standard Lateral Separation rule is 3nm but is sometimes 5nm.

These systems go off when aircraft are converging towards the same piece of airspace. If this was over Luton, then these aircraft could be in "the stack", properly called a Holding Pattern. This is a racetrack-shaped flight path using an electronic beacon.

At busy airports, aircraft arrive by joining the stack of other aircraft 1000ft higher than the top one already there. Everyone circles at a level altitude until the bottom one lands and then they all move down a 1000ft and so on. The TCAS system will only go off if aircraft flying straight and level get closer than 850ft vertically or if the computers calculate they are climbing/decending towards one another. TCAS not only looks after its own aircraft but it talks to the TCAS on all the aircraft around it. They coordinate their messages and will tell one aircraft to climb and the other to descend to avoid a computed collision. Clever stuff.

Morgan is on the money with the relative sizes of the aircraft. Vertical separation only has to be 1,000ft so they could be that close legally and safely. You can imagine one of those big 1,000mm lens at the soccer game being pointed straight up at two turning aircraft that are quite safely only 1000ft apart, this photo is dramatic but not scary. Just another aviation day at the office.

Brett

Message edited by author 2006-01-29 17:36:18.
01/29/2006 05:17:33 PM · #14
Originally posted by Morgan:

This image is a bit odd, but I also find the range variance difficult to believe. If the JAL is a 777-200 then it is about 209 feet or 64 metres in length. Whereas, if the DHL is a 737, then it is about 102 feet or 31 metres in length. This is a 2:1 ratio in size. But, that does not seem to calculate to validate this image.


How can you tell ... without knowing the distance from the observer to the first plane?

The further away from the observer the two planes are, the less the 2.5 mile separation will matter as far as apparent subject size goes.

A simply imagination exercise without using any math (except to say that we always keep the two planes 2.5 miles apart): if the shorter plane is only 100 feet away, and the larger plane is 2.5 miles away, then the larger plane is going to appear *tiny* by comparison. Now move the shorter plane out a mile and compare the relative sizes again. How about moving the shorter plane 5 miles away? Now what is the relative size of the longer plane?

See? Without knowing the distance from the observer to the first plane, you can't really judge the distance between the planes based on their relative sizes. Their true relative size only equals their apparent relative size when they are the exact same distance from the observer.
01/29/2006 05:26:21 PM · #15
Very grainy, soft focus, perspective is flat and DNMC --- 2

:-P


01/29/2006 05:36:56 PM · #16
I was an Air Traffic Controller for 16 years, and I assure you that two planes in that environment can get a lot closer that 2.5 miles without any compromise of safety or rules. Very often, when weather and visibility permits, air traffic controllers apply visual seperation between two aircraft, meaning that the "pilot of at least one of the aircraft has the other aircraft in sight and accepts responsibility for seperation" (to quote the actual rule from memory after 7 years).

By the way, Kiwipix seems to have great deal of knowledge of how the system works.
01/29/2006 05:38:57 PM · #17
So much for my post...I still think you are misinterpreting the statement...which makes all this discussion irrelevant.
01/29/2006 05:45:59 PM · #18
Originally posted by Alienyst:

So much for my post...I still think you are misinterpreting the statement...which makes all this discussion irrelevant.

Not at all, read carefully the detail.

The whole point is that the statement that they should be 2.5 miles apart is totally incorrect. The aircraft could be 1,000ft apart one on top of the other and be both legal and safe.

So what we're saying (thanks Yakatme) is that your thinking "... obviously one or both strayed from its flight path."... isn't the case here.

Brett
01/29/2006 05:48:13 PM · #19
Originally posted by Alienyst:

The spokesman said there was no question that either aircraft had strayed from its proper path, which should mean there was a distance of some two and a half miles between them.

I think you are misinterpreting...the statement says they SHOULD be that far away from each other, not that they ARE that far away from each other. If they stayed on their proper path they should be 2.5 miles apart but obviously one or both strayed from its flight path.

So much for my post...I still think you are misinterpreting the statement...which makes all this discussion irrelevant.


They COULD be that far away from each other and seem to be closer due to the difference in size and the photographer perspective.

They don't NEED to be that far away from each other if they are:
1) Using visual seperation
2) On approach to parallel runways seperated by the appropriate distance (something like 2,500 feet here in the U.S.) and conducting an instrument approach.
3) Or, using vertical seperation of 1000 ft as Kiwipix pointed out.

Message edited by author 2006-01-29 18:06:32.
01/29/2006 06:04:26 PM · #20
Originally posted by deapee:

looks like 2.4 miles to me, personally.


2.47
01/29/2006 06:19:50 PM · #21
I still think you are misinterpreting. The statement says that if they were on their correct flight path they would be 2.5 miles apart but since one or more of them strayed from said flight paths they are not but that no close encounter took place even though they were closer than they should have been to each other.
01/29/2006 07:23:07 PM · #22
Originally posted by bpickard:

I know men are prone to overestimating small distances, but 2.5 miles???!!

I don't believe the jets are of sufficiently different sizes to explain this, but please someone persuade me otherwise...


It is a fact that men are better at judging distances than women:)
edit*I know your a man but it doesnt matter:))

Fact:)

Message edited by author 2006-01-29 19:24:32.
01/29/2006 07:35:19 PM · #23
Originally posted by polkop:

Originally posted by bpickard:

I know men are prone to overestimating small distances, but 2.5 miles???!!

I don't believe the jets are of sufficiently different sizes to explain this, but please someone persuade me otherwise...


It is a fact that men are better at judging distances than women:)
edit*I know your a man but it doesnt matter:))

Fact:)


The learned prof. that they quote in that article is Ali G's dad....FACT.
01/29/2006 07:40:17 PM · #24
Originally posted by dwterry:



See? Without knowing the distance from the observer to the first plane, you can't really judge the distance between the planes based on their relative sizes. Their true relative size only equals their apparent relative size when they are the exact same distance from the observer.


You could, however, judge the minimum distance the planes are apart. If you assume the obvserver is right at the first plane (obviously not true), you should be able to figure out the distance the two planes are apart from their ratios. This distance should only get bigger the further the observer is back from the scene.
01/29/2006 07:52:43 PM · #25
What about the focal lenght of the lens. Long focal lenght lens compress the distance between two objects
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