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

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 ?

Answer 1

[Roger Stafford]

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);

[Priya]

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]

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.

Answer 2

[Iain]

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)

[jaya prakash]

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]

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