# Drawing Ellipses 4

Posted by **Brett Shoelson**,

Brett's Pick this week is ellipse, by David Long.

I've blogged before about fitting circles, and about simply drawing circles. And I've blogged about fitting ellipses. I like the general utility of functionality that facilitates those common tasks. Today, I complete the suite with a Pick that trivializes the drawing of an ellipse.

David's syntax is quite nice:

`h=ellipse(ra,rb,ang,x0,y0,C,Nb);`

There are defaults for all of the inputs (you'd get a circle of radius 1, plotted at [0,0]), but most usefully, you would
specify, at a minimum, the semi-major (`ra`) and semi-minor (`rb`) axes lengths, the desired angle, and the coordinates of the center (plus, optionally, the color and the number of points
used in the construction).

Remember Spirograph? Here's a fun little graphic I created using David's ellipse function, and another previous pick, distinguishable_colors:

colors = distinguishable_colors(20); n = 20; angles = linspace(0,2*pi,n); h = zeros(n,1); for ii = 1:n h(ii) = ellipse(2,1,angles(ii),0,0,colors(ii,:)); end axis equal axis off set(h,'linewidth',2) set(gcf,'color','w')

As always, comments to this blog post are welcome. Or leave a comment for David here.

Get the MATLAB code

Published with MATLAB® 7.13

**Category:**- Picks

## 4 CommentsOldest to Newest

**1**of 4

Beautiful!!

**2**of 4

hi, i want to draw an ellipse around objects in image, first i use background subtraction and earn an binary image, then by using [LABELED,NUM] = bwlabeln(I);

, regionprops, i draw a bounding box around each of objects in image, now i want to draw an ellipse around objects, i use steve’code on http://blogs.mathworks.com/steve/2010/07/30/visualizing-regionprops-ellipse-measurements/#comments but my separate objects lie in on ellipse and just draw one ellipse for all objects, i do not know what must i do? please help

**3**of 4

Sahere, If I understand your question, you might be able to use the position you calculated with Regionprops->BoundingBox as an input to:1) the MATLAB function RECTANGLE (which allows you, by controlling the curvature, to create ellipses; 2) a MATLAB ellipse annotation object; or 3) an Image Processing Toolbox IMELLIPSE object.

Cheers,

Brett

**4**of 4

Sahere, If I understand your question, you might be able to use the position you calculated with Regionprops->BoundingBox as an input to:1) the MATLAB function RECTANGLE (which allows you, by controlling the curvature, to create ellipses; 2) a MATLAB ellipse annotation object; or 3) an Image Processing Toolbox IMELLIPSE object.

Cheers,

Brett

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