21

I have a site and want to draw an indicative line in a 5km buffer around the centre of the site. So I want to draw a circle with a radius of 5km. I have a tool for drawing circles and ellipses and rectangles squares and spirals.

None of these let me state the centre point and the radius.

19

As commented by @Roy, you could make a point in layer and then buffer it into a new layer.

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  • Cheers. That is exactly what I wanted. Simple answer for a simple question. Panic had blinded me! – Ger Jul 16 '12 at 9:01
  • The workflow I have recently been using is to create the point in a Memory Layer, create the buffer into a shapefile saved in a temporary location, then copy and paste the polygon into the final layer. A bit long but works OK. – Willy Jul 27 '12 at 10:14
3

With mmqgis plugin you can convert your geometry type to centroids :

Plugins > mmqgis > modify > convert geometry type

And then just create buffers on shapes (through Vector > Geoprocessing tools) and precise the desired radius.

You got it

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2

I did something similar - need to draw 5km circles around a set of points meeting some criteria. I solved the problem using styles:

  1. Create a Symbology rule for the layer (in my case ": "field" is not null
  2. For the symbol, define a 'Simple Marker"

    • Size 10000.0 (the size is diameter, not radius
    • Units, select "Meters at Scale"
    • Fill color: Transparent

Voila! A range ring at true map scale.

I'm using QGis 3.10, which is much newer than when this question was originally asked.

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0

While developing a standalone qgis application, I shot help from QGIS Python Plugins Repository many times and it is very helpful. For drawing different geometries like Rectangle, Circle, Oval and Ellipse etc. this plugin is of great help.

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  • 1
    Unfortunately, that plugin has a problem: THIS PLUGIN IS NO LONGER ACTIVELY MAINTAINED. PLEASE UPDATE TO FIX A CRITICAL BUG THAT SLOWS DOWN QGIS AND CONSIDER TO DEINSTALL THE PLUGIN AND USE CADDIGITIZE INSTEAD – Stu Smith Jan 18 at 1:22
0

Possible by means of the "Rectangles, Ovals, Diamonds" geoalgorithm from the QGIS's Toolbox, using 'Ovals', either fixed or variable.

example

Note: That both 'Width' and 'Height' parameters have to be equal.


References:

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0

Consider also using "Geometry Generator" which contains a function make_circle($geometry, 100), see image below.

example

function make_circle
Creates a circular polygon.

Syntax
make_circle(center,radius[,segment=36]…)
[ ] marks optional components

Arguments
center center point of the circle
radius radius of the circle
segment optional argument for polygon segmentation. By default, this value is 36

Examples
geom_to_wkt(make_circle(make_point(10,10), 5, 4))'Polygon ((10 15, 15 10, 10 5, 5 10, 10 15))'
geom_to_wkt(make_circle(make_point(10,10,5), 5, 4))'PolygonZ ((10 15 5, 15 10 5, 10 5 5, 5 10 5, 10 15 5))'
geom_to_wkt(make_circle(make_point(10,10,5,30), 5, 4))'PolygonZM ((10 15 5 30, 15 10 5 30, 10 5 5 30, 5 10 5 30, 10 15 5 30))'

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