gnuplot-info

[Gnuplot-info] Plotting lines represented by (r, theta)

[James00007 <ach...@gm...>]

Hi,

I needed to plot straight lines and I can do this generally using the form
y=mx+c

However, almost-vertical lines give rise to unbounded values of m and c and
hence
they can not be plotted. For this reason, I have to represent lines the
Hough Transform way i.e (r, theta)

How can I plot lines that are represented by (r, theta)? This is just a
representation and not an equation.

Thanks
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Re: [Gnuplot-info] Plotting lines represented by (r, theta)

[Thomas S. <t.s...@fz...>]

you may use 'parametric mode'
http://www.gnuplot.info/docs_4.2/gnuplot.html#x1-14400034.4


James00007 wrote:
> 
> Hi,
> 
> I needed to plot straight lines and I can do this generally using the form
> y=mx+c
> 
> However, almost-vertical lines give rise to unbounded values of m and c
> and hence
> they can not be plotted. For this reason, I have to represent lines the
> Hough Transform way i.e (r, theta)
> 
> How can I plot lines that are represented by (r, theta)? This is just a
> representation and not an equation.
> 
> Thanks
> 

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Re: [Gnuplot-info] Plotting lines represented by (r, theta)

[Thomas S. <t.s...@fz...>]

a simple example:

xoffset=1.
yoffset=3.
set zeroaxis
set parametric
set xrange [-4:6]
set yrange [-2:8]
set trange [-4:4]
set angles degree
fx(t,phi)=xoffset+t*sin(phi)
fy(t,phi)=yoffset+t*cos(phi)
plot for [i=0:359] fx(t,i) , fy(t,i) notitle


Hi Thomas,

Thanks for help again...but I`m afraid I need more of it!

I`ve had a look at parametric mode and I can plot vertical lines using this
example:
http://t16web.lanl.gov/Kawano/gnuplot/parametric-e.html

But I need to plot a nearly vertical line through a point (x,y) with a
(steep) gradient of m.
Do you have any idea how the plot command will look like now (taking into
account the point (x,y) and gradient m?)

Hope I`m not asking too much!

Thanks


Thomas Sefzick wrote:
> 
> you may use 'parametric mode'
> http://www.gnuplot.info/docs_4.2/gnuplot.html#x1-14400034.4
> 
> 
> 

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Re: [Gnuplot-info] Plotting lines represented by (r, theta)

[James00007 <ach...@gm...>]

Hi,

The script does not work, i.e 

plot for [i=0:359] fx(t,i) , fy(t,i) notitle

gives an error message.

I didnt know that for statements existed in gnuplot but it may be that u
just gave my the pseudo code.
Guess I　have asked you enough and need to do a few things myself!



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Re: [Gnuplot-info] Plotting lines represented by (r, theta)

[James00007 <ach...@gm...>]

Hi Thomas,

Thanks for help again...but I`m afraid I need more of it!

I`ve had a look at parametric mode and I can plot vertical lines using this
example:
http://t16web.lanl.gov/Kawano/gnuplot/parametric-e.html

But I need to plot a nearly vertical line through a point (x,y) with a
(steep) gradient of m.
Do you have any idea how the plot command will look like now (taking into
account the point (x,y) and gradient m?)

Hope I`m not asking too much!

Thanks


you may use 'parametric mode'
http://www.gnuplot.info/docs_4.2/gnuplot.html#x1-14400034.4


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Re: [Gnuplot-info] Plotting lines represented by (r, theta)

[Thomas S. <t.s...@fz...>]

you are using an older version of gnuplot, not the actual one.
use this command instead:

plot fx(t,359.) , fy(t,359.) notitle, fx(t,0.) , fy(t,0.) notitle, fx(t,1.)
, fy(t,1) notitle


James00007 wrote:
> 
> 
> Hi,
> 
> The script does not work, i.e 
> 
> plot for [i=0:359] fx(t,i) , fy(t,i) notitle
> 
> gives an error message.
> 
> I didnt know that for statements existed in gnuplot but it may be that u
> just gave my the pseudo code.
> Guess I　have asked you enough and need to do a few things myself!
> 
> 
> 
> 

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Re: [Gnuplot-info] Plotting lines represented by (r, theta)

[James00007 <ach...@gm...>]

Thanks a lot for all the help. I was able to do what I needed to.

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Re: [Gnuplot-info] Plotting lines represented by (r, theta)

[Hans-Bernhard B. <HBB...@t-...>]

James00007 wrote:

> I am doing some other plotting the in the same script/plot but those
> functions are *not*
> in parametric mode whereas this particular plot requires parametric mode.
> 
> Is there a way to plot both kinds of functions in the same plot? 

Of course.  Any function f(x) is representable as a parametric curve
(t, f(t)), or in case you need the x range to be different from the t range:

	(my_x(t), f(my_x(t)))

Lesson to be learned: functions don't care about the name of their 
arguments.  It doesn't _have_ to be 'x'.