gnuplot-info

[Gnuplot-info] fit and plot problem

[Amir S. <ami...@gm...>]

Hi to you all,
I am trying to fit some discrete data to a circle and plot the
results. I have produced this script

------------------------------------------------------------------------------------------------------------
set terminal wxt enhanced
set fit logfile "Y:\\User.ASH\\controllo foratura SM ring\\Pesatura
21_07\\plots\\fitpuntoMED.log"
set size square
set samples 10000
set grid xtics ytics

#fit centers
g(x,y) = (x-a)**2 + (y-b)**2 - R**2
a=0.1
b=0.1
R = 1000
fit  g(x,y) "Y:\\User.ASH\\controllo foratura SM ring\\Pesatura
21_07\\plots\\puntoMED.txt" using 1:2:(0.001):(0.001) via a, b,R
set label 1 "Fitted Circle:\nR = R\nX_C = 0\nY_C = 0" at 390, -0.11, 0.375
plot "Y:\\User.ASH\\controllo foratura SM ring\\Pesatura
21_07\\plots\\puntoMED.txt" title "Median Point (mm)" with points pt 1
lt 7, \
g(x,y) title "Circular fit"
show grid

------------------------------------------------------------------------------------------------------------

the fit run smoothly but the plot does not, producing this output:
 "Y:\User.ASH\controllo foratura SM ring\Pesatura
21_07\plots\fitpuntoMED.p", line 19: undefined variable: y
where line 19 is:
g(x,y) title "Circular fit"

what I am doing wrong?

Thank you
Amir

Re: [Gnuplot-info] fit and plot problem

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

On 29.07.2010 16:37, wrote Amir Sabbagh:
> set fit logfile "Y:\\User.ASH\\controllo foratura SM ring\\Pesatura
> 21_07\\plots\\fitpuntoMED.log"

set fit logfile 'Y:/User.ASH/controllo foratura SM ring/Pesatura 
21_07/plots/fitpuntoMED.log'

would type so much easier...

And if you put a

   cd 'Y:/User.ASH/controllo foratura SM ring/Pesatura 21_07/plots'

at the beginning of the file, you can save even more needless typing.

> set label 1 "Fitted Circle:\nR = R\nX_C = 0\nY_C = 0" at 390, -0.11, 0.375

You'll want to change that to get the actual fit results into the label 
string.

> plot "puntoMED.txt" title "Median Point (mm)" with points pt 1 lt 7, \
> g(x,y) title "Circular fit"

> what I am doing wrong?

You're trying to use the 2D plot command to display a 3D function.  You 
want to use 'splot' instead.

Re: [Gnuplot-info] fit and plot problem

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

On 30.07.2010 10:27, wrote Amir Sabbagh:

> i need  a 2D plot for the circular fit, something like the "desired
> plot" attached. I think I am messing with the fitting function. Since
> I have a 2D set of points, i would like to have a 2D plot for the fit.

So g(x,y) is not the function you actually want to plot.  You want to 
plot the implicit curve defined by g(x,y)==0.  Your best bet for that 
would be parametric mode, plotting a circle with the properties found by 
fit:

	set parametric
	set trange [0:2*pi]
	plot 'data.txt', xa+R*cos(t), ya+R*sin(t) title "fit"


> Another point: I have tryied to pass the value of the variable "R" to
> the label with no success. Is it possible?

Yes.  See "help set label", particularly its mention of sprintf.