Drawing a circle between a centre point and one on the circumference is a common requirement in working up geometric patterns. If you need lines parallel to a radial line, or indeed any line at a fixed distance from another point, you need to draw a circle as a construction guide. the figure below will never be destined for design greatness, but it shows how they could be used:
The turquoise circles define the green parallel lines, and also the smaller green hexagon inside the black one. Drawing circles from a centre is what compasses do, yet Inkscape doesn’t have a tool to do it easily.
There is a way around this, though, that I picked up from this forum post. The poster’s method isn’t very clear, but in very brief summary, you need to construct a 3 point or 2 line-segment polyline with its nodes equidistant from the centre point, then use Render → Draw from Triangle … → Circumcircle to construct the circle. Simple? Um …
Okay, dodgy animation and point by point explanation coming up. With cusp, intersection and centre snapping all enabled:
- Draw two points: one for the centre, one on the circumference
(I usually draw a short diagonal line as the pointand snap to the cusp node, as they are unobtrusive but easy to pick up the rotation centre.)
- Click on the circumference point to select it
- Click on the circumference point again to select the rotation centre and handles
- Move the rotation centre of the point to the centre of your circle
- Duplicate the point (Ctrl+D)
- Rotate the point 90° (Object → Rotate 90° CW)
- Duplicate the new point (Ctrl+D)
- Rotate the new point 90° (Object → Rotate 90° CW)
(You should now have three points arranged around a semicircle)
- Draw two straight line segments through the three points
- Select the line
- Render → Draw from Triangle … → Circumcircle — and there’s your circle.
There’s probably another way to do this by creating a point (Ctrl+click in Line mode) giving it a line width, setting rounded line ends, then doing Path→Stroke to Path to get a buffer around the point, but I can’t work out how to do this reliably.
Oh, and the patten I made from the construction? Well, it might look okay on a paper towel …