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Re: line drawing knowing angle and a point [message #40123]

Wed, 21 July 2004 13:13

btt
Messages: 345
Registered: December 2000

Senior Member

Francois Leduc wrote:

> Hello,
>
> I there a fast way to draw a line in an image knowing 1) the angle of the
> line (with the vertical direction) and 2) a point belonging to the line ?
>

Hello,

Assuming that you angle is acute, the following should work.

y = a + bx
p = point at x,y
theta = angle in radians

b = atan(!pi - theta)
a = py - b * px

theta = 0.4 & p = [11,3]
b = atan(!pi - theta) & a = p[1] - b * p[0]
x = findgen(40)-20 & y = a + b * x
plot, x,y
plots, p[0], p[1],/data, psym = 5

Ben

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