Mini-tut request: piece of arc

[amoore]

Ok, guys, I'm sure there's an easier way to accomplish this piece of arc than I've found so far. How would you do it?

What I've got looks fine at icon-size, but the flaws will become obvious when I have to use it in other contexts. Besides, I'd rather know how to do it right. http://www.talkgraphics.com/images/smilies/smile.gif

[amoore]

Ok, guys, I'm sure there's an easier way to accomplish this piece of arc than I've found so far. How would you do it?

What I've got looks fine at icon-size, but the flaws will become obvious when I have to use it in other contexts. Besides, I'd rather know how to do it right. http://www.talkgraphics.com/images/smilies/smile.gif

[jclements]

There's probably a quicker way, but one method would be to create two circles (one for the inner diameter of the arc and the other for the outer diameter) and align then centrally.

Draw a vertical line and a horizontal line (longer than the outer diameter) and align them centrally to the circles; their intersection defines the center of circles and provides a "pivot" point.

Cut the vertical line in half using the horizontal line. Delete the bottom half of the old vertical line.

Cut a hole in the larger circle using the smaller circle.


Duplicate the remaining vertical line a few times. Now, with the snapping magnet on, move the rotation points of the lines to its bottom node (the center of the circle). Use the Info Bar to rotate (in degrees) each copy of the line to the approriate angle.

Finally, use the lines to slice up the "donut".

[amoore]

Thanks, John! That worked very well.

I'd done most of that (among other things http://www.talkgraphics.com/images/smilies/biggrin.gif). What was hanging me up was that the original was more of an ellipse than a circle, and I just couldn't seem to match the arc. Following your instructions, I finally got the circles to come close enough to the right arc that no one will notice the difference.

[diniel]

I'd draw the outer circle, clone (CTRL+K) it, then hold shift while you drag its corner blobs to resize it (equally both sides). Clone it again and manually set its width to say 0.01pix - so you end up with two circles and effectively a dot in the middle.

Turn on Snap to Objects (magnet on toolbar) and draw your first line from the circle edge to the middle, then out again to the edge. Do this by eye, or do it once then flip the line to be sure it is on the same angle.

Repeat with another pair of lines, and you end up with the attached. Group the two big circles, then select a 'V' (group the two lines if you did outside-centre-outside with two lines instead of one with three points) and Slice (CTRL+4).

Slice again with the other lines, and then start ungrouping everything and see what you're left with.

To be more accurate you can change the point of rotation for your copied/cloned lines by clicking the line twice to see its rotate control handles, then moving the 'target' that you see in the middle of the line to the centre dot in the middle of your circle. This obeys the Snap to Object mode, so it will latch onto the centre point, or the end of your line.

If you had to use more than two circles, you could use the Contour tool, set the number of steps, and then convert to shapes/ungroup.

[roman]

Daniel. Nice idea. Now just show grid and snap to grid would add the desired accuracy.

[amoore]

Thanks, Daniel, that worked very well except for the grouping thing. AFAICT, the small circle must explicitly slice the big circle. As for the lines, if you slice with a group of lines, only one line actually slices, and it extends itself virtually across and through the shape. Convert the lines to shapes and then group and slice, and you get the results you wanted, but not as a group of shapes. It's a single shape you can break into the right parts. [Sorry if this isn't very clear. I've been interrupted repeatedly, and had to start over twice. Don't have time to go back and clean it up.]

Thanks also for the tip about the contour. That works perfectly for getting the arc out of an ellipse.

All in all, between you and John, it won't take me nearly so long to do the next one. http://www.talkgraphics.com/images/smilies/biggrin.gif

[roman]

arc tut optimised, (based on Daniel's draw-a-line idea)


roman

[amoore]

Better & better! Very elegant indeed, Roman. http://www.talkgraphics.com/images/smilies/smile.gifhttp://www.talkgraphics.com/images/smilies/smile.gifhttp://www.talkgraphics.com/images/smilies/smile.gifhttp://www.talkgraphics.com/images/smilies/smile.gifhttp://www.talkgraphics.com/images/smilies/smile.gif

Thanks, guys!