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Home > Draw > Circle: Center Radius
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Circle: Center Radius (tool)A circle whose radius tracks another object's size.
Menu: Draw > Circle: Center Radius | Node: Circle: Center Radius | In depth: Circles & arcs
Click the center, then click something that already has a size: a segment, a circle, or an arc. The new circle takes its radius from that object and keeps taking it.
This is transferring a length rather than setting one. A physical compass does it by stepping the points off a drawn edge and swinging without changing the setting; here the transfer stays live, so when the source changes the circle changes with it.
A circle drawn from a center and a rim point has a radius of its own, and nothing else in the drawing knows about it. A compass circle has no radius of its own at all: it asks its source every time.
That is what makes equal-radius work hold together. Build six circles off one segment and they are not six circles that happen to match, they are six circles that cannot stop matching. Stretch the segment and all six follow. In pattern work, where a repeat depends on a set of circles staying the same size as each other, this is the difference between a figure that survives being adjusted and one that has to be rebuilt.
The source can be any of three things, and each reads the obvious way: a segment gives its length, a circle gives its radius, an arc gives its radius.
The center click places a point the way the Point tool does, so the circle can be centered on a crossing and stay there.
The second click has to land on a real object. If nothing size-bearing is under the cursor the tool says so and waits, rather than guessing a radius from where you clicked.
It also works straight from a selection: select a point and a segment, circle, or arc, then pick the tool, and it builds from those without any clicking.
The wiki called this page Compass Circle for a long time, and its address still does, so older links and bookmarks keep working. The title now matches the app, which calls the tool and the node Circle: Center Radius.
Not to be confused with Compass: Radius, which is a construction tool: it also sizes itself from an existing object, but then goes straight into tick mode and retires the circle when you finish.
< Previous: Circle: Center Point | Next: Circle: Through 3 Points >
- In the node graph: Circle: Center Radius - build the same circle as a node.
- Circle: Center Point: a radius of its own, set by a rim point.
- Compass: Radius: the construction-tool version, with ticks.