Circle Hell

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  • Talon
    #1

    Circle Hell

    Hi all,

    I am new to Tk, so please bear with me. I need someone better at math
    than me to help me figure this out. I am drawing multiple arcs on the
    same circle. All arcs start at 90 and have varying negative extents
    (different colors, goes all the way around. Represents a microbial
    genome). So now that my arcs are drawn, I would would like to draw a
    line, 25 pixels long that starts on the circle at the endpoint of each
    of the arcs, and looks like an extension of the radius extending above
    the circle. Then I would like to print text at the end of this line. So
    my question is how do I dynamically calculate the line coordinates?
    Circle size is fixed, number of arcs and their extents are variable.

    Code for drawing arc;
    $x1,$y1 = 25
    $x2,$y2 = 775
    $xcenter = $x2/2 + $x1;
    $ycenter = $y2/2 + $y1;

    $canvas->createArc($x1, $y1,$x2,$y2,
    -width=>10,
    -outline=>$color s[$color],
    -style=>'arc',
    -start=>90,
    -extent=>-$actual_angle,
    -tags=>$myorfs{$ key}[1]);

    What I have so far to draw lines:

    $xstart = (cos($current_a rclength)*$radi us+$xcenter) /10;
    $ystart = (sin($current_a rclength)*$radi us+$ycenter) /10;
    $canvas->createLine($xs tart+$xcenter,
    $ystart+$ycente r,
    $xstart+($xstar t*0.01)+$xcente r,
    $ystart+($ystar t*0.01)+$ycente r);

    This draws an oval of lines, inside the orginal circle, with the line
    length having sin periodicity around the circle. Can anyone improve my
    math so that I can get the lines placed properly with the proper length?

    Please email me directly as well as respond to the list. Thanks so much
    in advance.

    --Math Challenged Mark

    Mark.Evans.B@ba yer.com
    Tags: None
    • Bengt Richter
      #2
      Re: Circle Hell

      On Thu, 04 Sep 2003 07:55:18 -0700, Talon <talon34@hotmai l.com> (by way of Talon <talon34@hotmai l.com>) wrote:
      [color=blue]
      >Hi all,
      >
      >I am new to Tk, so please bear with me. I need someone better at math
      >than me to help me figure this out. I am drawing multiple arcs on the
      >same circle. All arcs start at 90 and have varying negative extents
      >(different colors, goes all the way around. Represents a microbial
      >genome). So now that my arcs are drawn, I would would like to draw a
      >line, 25 pixels long that starts on the circle at the endpoint of each
      >of the arcs, and looks like an extension of the radius extending above
      >the circle. Then I would like to print text at the end of this line. So
      >my question is how do I dynamically calculate the line coordinates?
      >Circle size is fixed, number of arcs and their extents are variable.
      >
      >Code for drawing arc;
      >$x1,$y1 = 25
      >$x2,$y2 = 775
      >$xcenter = $x2/2 + $x1;
      >$ycenter = $y2/2 + $y1;
      >
      >$canvas->createArc($x1, $y1,$x2,$y2,
      > -width=>10,
      > -outline=>$color s[$color],
      > -style=>'arc',
      > -start=>90,
      > -extent=>-$actual_angle,
      > -tags=>$myorfs{$ key}[1]);
      >
      >What I have so far to draw lines:
      >
      >$xstart = (cos($current_a rclength)*$radi us+$xcenter) /10;
      >$ystart = (sin($current_a rclength)*$radi us+$ycenter) /10;[/color]
      These look ok except dividing by 10, assuming the units for the angle are ok (degrees vs radians?)
      Dividing by 10 seems weird here, so try leaving it out.
      [color=blue]
      >$canvas->createLine($xs tart+$xcenter,
      > $ystart+$ycente r,[/color]
      From above, xstart already has xcenter in it, so don't add it again. Same for ycenter.[color=blue]
      > $xstart+($xstar t*0.01)+$xcente r,
      > $ystart+($ystar t*0.01)+$ycente r);[/color]
      If you want to draw a 25-pixel line, where is the "25"? You just need to resolve the 25
      into x and y components and add them to your respective starting points, I would think.
      So UIAM the above becomes (giving a name to the 25-pixel length (assuming dimensions are in pixels)

      $tick_length = 25.0;

      $xstart = cos($current_ar clength)*$radiu s+$xcenter;
      $ystart = sin($current_ar clength)*$radiu s+$ycenter;

      $canvas->createLine($xs tart,
      $ystart,
      $xstart+ cos($current_ar clength)*$tick_ length,
      $ystart+ sin($current_ar clength)*$tick_ length);
      [color=blue]
      >
      >This draws an oval of lines, inside the orginal circle, with the line
      >length having sin periodicity around the circle. Can anyone improve my
      >math so that I can get the lines placed properly with the proper length?
      >
      >Please email me directly as well as respond to the list. Thanks so much
      >in advance.
      >
      >--Math Challenged Mark
      >
      >Mark.Evans.B@b ayer.com[/color]

      HTH

      Regards,
      Bengt Richter

        Comment

        • Mark Carter
          #3
          Re: Circle Hell

          > $xstart = (cos($current_a rclength)*$radi us+$xcenter) /10;[color=blue]
          > $ystart = (sin($current_a rclength)*$radi us+$ycenter) /10;[/color]

          I wouldn't be using lengths of arcs, if I were you. And that division
          by 10 looks a bit odd, too.

          Given a circle of radius r, if the arc stops at an angle theta to the
          horizontal (measured anticlockwise from the east), then the point on
          the circle is:
          x = xcentre + r * cos(theta)
          y = ycentre + r * sin(theta)

          If you want to know the point at a distance 25 from the circle, simply
          substitute (r + 25) in the formula above.

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