CODEWITHSUNDEEP
javascriptmath
isso11
isso11

Reputation: 23

Intersection of two Moving Objects

I'm trying to use the answer provided here: Intersection of two Moving Objects with Latitude/Longitude Coordinates

But I have some questions..

What is this angle:

var angle = Math.PI + dir - target.dir

I was thinking that the angle that should be used in the law of cosines is already "alpha or target.dir".. What is that line doing? Also in these two steps:

 var x = target.x + target.vel * time * Math.cos(target.dir); 
 var y = target.y + target.vel * time * Math.sin(target.dir);

Shouldn't the code be using the angle between x- or y-axis and the target velocity vector? Why is the author using alpha here?

enter image description here

Upvotes: 2

Views: 670

Answers (1)

m69 ''snarky and unwelcoming''
m69 ''snarky and unwelcoming''

Reputation: 12324

What is this angle:

var angle = Math.PI + dir - target.dir

The variable named angle is indeed the angle alpha. Because the direction dir is the direction from chaser to target, and we need it the other way round for this calculation, we add π to it before we subtract target.dir.

Maybe using the word angle as a variable name was a bit vague; I'll change it to alpha, the name I used for this angle in the images.

Shouldn't the code be using the angle between x- or y-axis and the target velocity vector? Why is the author using alpha here?

var x = target.x + target.vel * time * Math.cos(target.dir);  
var y = target.y + target.vel * time * Math.sin(target.dir);

We are indeed using target.dir, which is the direction of the target, i.e. the angle between the x-axis and the target vector, to calculate the coordinates of the interception point, and not the angle alpha.

Upvotes: 1

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