How to plot a line parallel to a line with a distance of d between them ?

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I have a line whose slope is m and y-intercept is c.
I wan to make a parallel line above and below to this line with at a distance of d between them.
Can anyone help ?

Answers (2)

Roger Stafford
Roger Stafford on 5 Mar 2014
My guess is that where Priya says "a parallel line above and below to this line with at a distance of d between them", the orthogonal distance between them is to be d, not the vertical distance. If so, the equations of the two lines would be:
Line above:
y = m*x + c + d*sqrt(1+m^2);
Line below:
y = m*x + c - d*sqrt(1+m^2);
  2 Comments
Priya
Priya on 5 Mar 2014
Hi,
The solution was simple. Actually the slope of the line parallel to a given line, will be same as that of the given line and the intercept will actually be +/- distance d.
Thanks for efforts everyone
Roger Stafford
Roger Stafford on 6 Mar 2014
Priya, I suggest you set m equal to a very large number such as m = 100, and make a plot of your three lines (using "axis equal") to see if a vertical displacement by d rather than an orthogonal one is what you are really after. The lines will look much closer together than your d value if a vertical displacement is used.

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Iain
Iain on 5 Mar 2014
For where you want to plot it:
x = 0:1:42;
m = 4;
c = -12;
Line 1 =
y1 = m*x + c
Line 2 (above by d)
y2 = m*x + c + d
Line 3 (below by d)
y3 = m*x + c - d
plot(x,y1,x,y2,x,y3)
  2 Comments
jaya prakash
jaya prakash on 2 Dec 2014
Hi
how could you tell that
x = 0:1:42; m = 4; c = -12;
for every line?
for example if i had a set of polygon points say a=[0 0;1 0;1 1;0 1] then how i will get a offset for a square with a distance d=0.1 ?
thanks in advance for helping
jaya prakash
jaya prakash on 2 Dec 2014
Otherwise i will keep my question in a simple way
i have a line from point a(0,0) to b(1,1)
how would i get a offset line at a distance d=0.1 on both sides ?
thanks in advance

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