[Gnuplot-info] piping data to gnuplot does most of what I want, but ......

[Mitchell T. <ze...@sh...>]

I'm using Windows 2000, and I've gotten good results except I can't get 
a parametric plot to display with a set of data points.   I'm using C, 
inspired by pdemo.c.  First, here's what works:

     gnuplot = _popen("pgnuplot.exe", "wb")
     setbuf( gnuplot, NULL );
     fprintf(gnuplot, "set title 'Best Trajectory So Far'\n");
     fprintf(gnuplot, "set size ratio -1\n");    /* for round circles */
     fprintf(gnuplot, "plot '-',");         /* so gnuplot accepts piped 
input */
     fprintf(gnuplot, "sqrt(10000.0-x*x), -sqrt(10000.0-x*x)\n");    /* 
parametric is better */
     for(i=0; i<count; i++)
            fprintf(gnuplot, "%8.2f %8.2f\n",point[i].x, point[i].y);  
/* pipe the data */
     fprintf(gnuplot,"e\n");   /* gnuplot needs this EOD signal */

That works fine.  The line with the 2 sqrt()s draws 2 circle arcs, so 
the result is a circle and a series of points.  That's what I want, 
except the circle has gaps and is of two colors.   I would prefer a 
parametric plot, but when I replace that line with the following it does 
not draw anything:

   fprintf(gnuplot, "set parametric\n");
   fprintf(gnuplot, "[-pi:pi] 100*sin(t), 100*cos(t)\n");
   fprintf(gnuplot, "unset parametric\n");

So, how can my C program draw a parametric plot followed by a bunch of 
points?

Thanks,

Mitchell Timin

-- 
"In theory, there is no difference between theory and practice.  In 
practice, there is."

http://annevolve.sourceforge.net is for those seeking something to do 
with their wetware.



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