an Image Magick Tute by Flo 
Arcs are trickier than the other Primitives to figure out. Placing their position accurately depends upon our being able to visualize the complete 360degree form, even when only part of it is showing.
So we must think about the right side of the curve (0 degrees, also 360 degrees), the bottom of the curve (90 degrees), the left side (180 degrees) of the curve and the top part (270 degrees) of the curve, even if we are drawing only any one part of this curve. Refer to the clock face below:
To Draw an Arc, we need to use 3 sets of numbers:
 1st Set:
 1st number = how far from image's left side the arc's left side extends;
 2nd number = how far down from image's top the arc's upper curve is (imaginary 360degree arc).
 2nd Set:
 1st number = how far from image's left side the arc's right side is;
 2nd number = how far down from image's top the arc's bottom curve is.
 3rd Set:
 1st number = how far from 0 degrees (clock position 3) the curve starts;
 2nd number = how many degrees (clockwise) around the curve the end of the arc extends.
DIRECTIONS
 Start with a 200x100 white xc background.
 Select Arc from the Primitive dropdown.
 Type the following numbers into the box: +10+10 +190+90 +0+180
Remember that you can use commas instead of plus signs: 10,10 190,90 0,180
 Fill Color=blank; Stroke Color=your choice; Stroke width=2
 Click on the Draw button.
Your Draw Arc should look like this:
MORE EXAMPLES


10,10 190,90 180,360 
50,10 150,90 160,20 


25,10 250,90 90,250 
150,30 190,85 215,45 
SUGGESTIONS FOR PRACTICE
 Make a 200x100 white xc background. In DrawArc, type in a set of numbers under the above examples. Then change ONLY ONE number, click on Draw and see what happens. Back up and change another number, see what happens this time. Keep doing this until you feel you have a better understanding of what each number does.
 Choose the numbers for the last example (the smallest quirky arc): 150,30 190,85 215,45 and make 4 examples for yourself with the following changes only:
 150,30 190,85 215,45
 150,30 190,85 215,45 (minus 215)
 150,30 190,85 215,45 (minus 45)
 150,30 190,85 215,45 (minus 215, minus 45)
Compare these 4 examples and you'll see 4 different arcs.
 Try Drawing an Arc and setting the Fill Color to a different color from the Stroke Color.
 Remember, we are limited only by our own imaginations.
Back to Flo's Image Magick Draw Tutes
 