How to draw an Arc in the direction you want? (with known radius, centre and angle)

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ErikJon Pérez Mardaras 2020-11-9

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编辑： ErikJon Pérez Mardaras 2020-11-10

I'm trying to draw an arc between 350º and 0º angles, but the point is that I would like to draw it in counter-clock wise. What is the general method of drawing an arc in matlab in the direction you want?

The code I have written is the following:

hold on
grid
axis equal
angini=350;				%initial angle of the arc in degrees
angfin=0;				%final angle of the arc in degrees
rangini=deg2rad(angini);		%initial angle of the arc in radians
rangfin=deg2rad(angfin);		%final angle of the arc in radians
centre=[0;0];				%centre of the arc
radius=10;				%radius of the arc
teta = linspace(rangini,rangfin);        
xco = centre(1)+radius*cos(teta); 	%x coordinates
yco = centre(2)+radius*sin(teta);      	% y coordinates
plot(xco,yco,'g')			%plot the arc

And the result, as you can see, is the following:

It drew the arc in a clockwise direction, not in a counterclock one. What is the general method of drawing an arc in matlab in the direction that you like?

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Answer 1

Steven Lord 2020-11-9

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https://ww2.mathworks.cn/matlabcentral/answers/642220-how-to-draw-an-arc-in-the-direction-you-want-with-known-radius-centre-and-angle#answer_539170

在 MATLAB Online 中打开

Use an ending angle of 360 degrees rather than an angle of 0 degrees. You can skip the deg2rad calls by using the degree-based trig functions cosd and sind. I also chose to change some of the variable names to make them a bit more descriptive. With those names you could argue the comments are unnecessary.

hold on
grid
axis equal
angleInitial=350;				%initial angle of the arc in degrees
angleFinal=360;				%final angle of the arc in degrees
centre=[0;0];				%centre of the arc
radius=10;				%radius of the arc
theta = linspace(angleInitial,angleFinal);        
xcoords = centre(1)+radius*cosd(theta); 	%x coordinates
ycoords = centre(2)+radius*sind(theta); 	% y coordinates
plot(xcoords,ycoords,'g')			%plot the arc

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ErikJon Pérez Mardaras 2020-11-9

编辑：ErikJon Pérez Mardaras 2020-11-9

Thanks for the repply, but I am looking for a general answer for a general issue. Imagine that, instead of wanting to draw an arc from 350º to 0º(or 360º) I would like to draw an arc from 170º to 220º but in a clockwise direction instead of a counterclock one (which is what Matlab would do in this case).

As you can see in the following image, Matlab draws me that arc in a counterclock wise direction.

Is the same case as before. How I could draw arcs in the directions I want? Is there any way?

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