how to find the distance?

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bsd
bsd 2011-9-18
Hai,
I have drawn a line between two points, I need to find the length(distance) of that line between those two points. Is there a command in matlab that could find the length(distance) of the line? Looking forward to hearing from you soon.
BSD

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回答（2 个）

Jan
Jan 2011-9-18
point1 = rand(1, 3);
point2 = rand(1, 3);
distance = norm(point1 - point2);
Or:
d = point1 - point2;
distance = sqrt(d * d');
Or with the fast C-Mex FEX: DNorm2, which operates on rows or columns of matrices also:
distance = DNorm2(point1 - point2);
  2 个评论
Michael Leung
Michael Leung 2011-9-19
bsd, I'm not sure in how many dimensions you are working in, but in 2D, and 3D, norm would be the function you are looking for.
It uses simple Pythagorean theorem to find the distance.
(I'm not sure if Pythagorean would apply in higher dimensions, I can not visualize how it would work! XD)
Jan
Jan 2011-9-19
The 2-norm (Euclidean norm) works in arbitrary dimensions. It is: SQRT(SUM(x.^2)). In my example SUM(x.^2) is implemented faster using the DOT product x*x', which is calculated by the fast BLAS library.

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Walter Roberson
Walter Roberson 2011-9-18
Use hypot
distance = hypot(point1 - point2);
This assumes, of course, that the line is a straight one and the measurement is in Euclidean geometry, and the distance metric is the Euclidean distance.
  2 个评论
Jan
Jan 2011-9-18
@Walter: The documentation you've linked to explains, that HYPOT needs two inputs. HYPOT(point1, point2) does also not measure the distance.
Walter Roberson
Walter Roberson 2011-9-19
Yes, you are right. But if you are working in 2d, then splitting the difference in two a and b components and using hypot() will generate more precise answers if the differences might be quite small, especially below sqrt(eps(0)) (approximately 1E-162)

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