If you only measure the outmost tips as Deino did, the photography distortion due to the angle won't matter, will it? I mean point does not distort, only lines and shapes distort.
J-20 5th Gen Fighter Thread VI
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Nice trigonometry problem! Only if we knew the angle and FOV involved.
vesicles
Colonel
I agree. For all intents and purposes, the J-20 is a Flanker-sized fighter. Its performance? We won’t know until the PLAAF gives us evidence.
that is valid in case we are trying to measure the length of a line such as the vertical stabilizer. But Deino's measurement was about the length of the plane from nose tip to tail booms' tips, both are points. The length between the two tips are not affected by the angle of the camera.
Here is my thought. The length of any vertical lines would be different depending on the position of the camera. But the length of any line on the horizontal plane is not affected.
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Yes they are.
Imagine looking at a pencil orthogonally and then diagonally. There will be a difference between the distance from one end of the pencil to the other end. Tilt it even further and the pencil's length disappears entirely and you'll be looking solely at the tip head on.
What you are saying is true IF there is no known reference. What Deino did was not measure J-20 alone, but use the known length of J-16 as a reference to calculate. When we move the viewing point, both their lengths change, but their relative lengths don't, therefor the measurement is reliable.
BTW, I updated my post #1086 to illustrate what I thought. I am aware that it does not demonstrate the reference length part that I am saying above.
@jobjed
Addition to #1088,
Let's say, we have two pencils. One is known to be 10cm long. The other is unknown. Put them parallel to each other (like J-20 and J-16). When moving our camera toward the tips, their visual lengths both reduce. But since we know one is 10cm, so the other is always x% of 10cm. The x remains constant and measurable, so we can get the absolute length of the other pencil.
Addition to #1088,
Let's say, we have two pencils. One is known to be 10cm long. The other is unknown. Put them parallel to each other (like J-20 and J-16). When moving our camera toward the tips, their visual lengths both reduce. But since we know one is 10cm, so the other is always x% of 10cm. The x remains constant and measurable, so we can get the absolute length of the other pencil.
They're not parallel. The J-20 is directly under the drone while the line of sight to the J-16 is slanted at ~20 degrees.
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