How can I draw a filled circle?
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I know the radius and the center coordinate of a circle
I want to fill this circle with black color
how can I do this?
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采纳的回答
Walter Roberson
2013-9-13
5 个评论
Will Reeves
2022-2-15
Yes please.. + 1 for that request. please implement "FaceColor" for a viscircles property! I need to draw thousands of circles in a plot...
Will Reeves
2023-6-21
Also, just for completness.. Is there a "quality setting" somewhere for rectangle (when curvature=1) that draws a circle instead of a load of straight lines?
for example:
更多回答(7 个)
Shahriar
2013-11-9
Very simple. The following will draw a filled circle at (1,1) with red color. Change it as you wish.
plot(1, 1, '.r', 'MarkerSize',69)
5 个评论
Image Analyst
2022-10-6
@Sathish Kumar and @Patriek Bruurs, that's correct. The marker size is relative to your screen or figure size or something. It is not relative to the scale used for your x and y axes. So zooming in and out will probably not change the marker size, and the marker size has nothing at all to do with the spatial calibration scale of your x and y. So for example if you wanted a big spot you'd use a markersize of, say, 100 regardless if your x and y axes went from 0-1 or from 0 to a billion. The marker size is NOT the diameter of the spot in units of your graph. So if your axis went from 0 to a billion you'd still use a marker size of 100, not a marker size of 30 million. Also zooming in or out of the axes does not change the marker size - you can imagine scenarios where if it did, it would be a disaster, with the marker covering up some small region you wanted to scrutinize.
Walter Roberson
2022-10-7
I did some measurements on my screen last night. To within measurement error, the spot size produced by plot() grew linearly -- for example spot size 1000 was twice as large as spot size 500. But I was not able to figure out what the units were; the units did not make sense in inches or mm or points. For example marker size 1000 was approximately 66.4 mm diameter -- between 66.1 and 66.8 (I cannot get my digital calipers flat on the screen and it is a judgement call about where exactly the bounds are.) (Admittedly, due to measurement error, it just might be the case that the spot size is slightly nonlinear.)
My display is a larger one, but is below the bounds at which MATLAB starts lying about resolutions
Image Analyst
2013-9-13
To create a 2D logical image of a solid circle (a disc), you can use code like this:
% Create a logical image of a circle with specified
% diameter, center, and image size.
% First create the image.
imageSizeX = 640;
imageSizeY = 480;
[columnsInImage rowsInImage] = meshgrid(1:imageSizeX, 1:imageSizeY);
% Next create the circle in the image.
centerX = 320;
centerY = 240;
radius = 100;
circlePixels = (rowsInImage - centerY).^2 ...
+ (columnsInImage - centerX).^2 <= radius.^2;
% circlePixels is a 2D "logical" array.
% Now, display it.
image(circlePixels) ;
colormap([0 0 0; 1 1 1]);
title('Binary image of a circle');
10 个评论
Sharne Fernandes
2022-8-21
@Image Analyst, could you suggest to me a way of adding more than 1 circles using these steps?
Thank you
Walter Roberson
2022-8-23
% Create a logical image of a circle with specified
% diameter, center, and image size.
% First create the image.
imageSizeX = 640;
imageSizeY = 480;
[columnsInImage rowsInImage] = meshgrid(1:imageSizeX, 1:imageSizeY);
% Next create the circle in the image.
centerX = [100 180 300];
centerY = [150 30 400];
radius = [100 20 50];
circlePixels = any((rowsInImage(:) - centerY).^2 ...
+ (columnsInImage(:) - centerX).^2 <= radius.^2, 2);
circlePixels = reshape(circlePixels, imageSizeY, imageSizeX);
% circlePixels is a 2D "logical" array.
% Now, display it.
image(circlePixels) ;
colormap([0 0 0; 1 1 1]);
hold on
scatter(centerX, centerY, 'r+');
hold off
title('Binary image of circles');
Chad Greene
2014-11-20
circles(x,y,radius,'color','black')
2 个评论
Image Analyst
2021-2-6
Now there is a viscircles function built in to the Image Processing Toolbox
viscircles([x, y], radius);
This can handle vectors of centers and radii, in addition to just one.
ABDULRAHMAN HAJE KARIM ALNAJAR
2018-8-8
编辑:Walter Roberson
2019-11-10
Simply, use the following command:
I = insertShape(I,'FilledCircle',[x y r],'color',[1 1 1],'LineWidth',5);
[x y] is the centre coordinates r is the radius
Note, you need Computer Vision Toolbox to run this command.
1 个评论
Walter Roberson
2019-11-10
This is a good routine to use if you have a matrix that you want to draw a circle into. It is not, however, a good routine to draw a circle on the display.
vatankhah
2013-9-13
编辑:vatankhah
2013-9-13
3 个评论
Will Reeves
2023-6-21
编辑:Will Reeves
2023-6-21
... but it seems as if this is fairly course angular resolution and are therefore not really circles. Please can this adjusted in a future release so that you can chose the angular precision?
Image Analyst
2023-6-21
@Will Reeves remember we're dealing with digital computers that use discrete values and don't have infinite precision. If you're really going to zoom way, way in, so much so that the circle has "kinks" in it because it's made up as very short line segments, you can make those line segments as small as you want by increasing the angular resolution in the code in the FAQ:
Anton
2014-9-24
编辑:Walter Roberson
2019-11-10
Use "area" command. Typically used to fill area under y=f(x) curve.
Using Rectangle command has 2 inconveniences: 1) They use figure axes, not the graph axes (see this submission for help http://www.mathworks.co.uk/matlabcentral/fileexchange/30347-sigplot/content/sigplot/sigplot/BasicFunctions/dsxy2figxy.m )
2) a consequence of 1 in fact: if you zoom or move the graph your circle will remain in "old" position and scale, which is annoying.
This is how you draw a filled circle of radius R at (x,y) in the axis of your graph using "area" command:
Ang = 0:0.01:2*pi; %angle from 0 to 2pi with increment of 0.01 rad. CircX=R*cos(Ang); CircY=R*sin(Ang);
h=area(X+CircX,Y+CircY);
set(h,'FaceColor',[.7 0 0]) %colour of your circle in RGB, [0 0 0] black; [1 1 1] white set(h,'LineStyle','none')
% unfortunately you have to remove the line: because circle is not a function strictly speaking. % "area" command tries to fill area below your function which leaves a line-artefact connecting your circle with X axis.
1 个评论
Walter Roberson
2019-11-10
? rectangle() uses data units, which are axes relative. It does not use figure units.
annotation() uses figure units though.
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