how to find the end of major and minor axis of an ellipsoid

Question

nadia nadi 2017-3-10

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/329193-how-to-find-the-end-of-major-and-minor-axis-of-an-ellipsoid

编辑： Walter Roberson 2017-4-21

在 MATLAB Online 中打开

Dear,

I have this information of an ellipse

a=29.2139; b=17.7345; xC= 43.9666; yC=42.9211; angle=29.7207;

can any one tell me why the end of the major and minor axis are not in the right place. I tried to rotate them using matrix H, but still it gives me wrong places. can any one help please.

Many thanks,

Nadia,

1 个评论
显示 -1更早的评论隐藏 -1更早的评论

Walter Roberson 2017-4-21

Please show your code.

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Image Analyst 2017-3-10

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/329193-how-to-find-the-end-of-major-and-minor-axis-of-an-ellipsoid#answer_258192

Looks like you forgot to apply your rotation matrix to the "g" coordinates.

2 个评论
显示无隐藏无

nadia nadi 2017-3-13

编辑：nadia nadi 2017-4-21

hello, thanks for replying. I applied but still gives me the wrong positions.

Image Analyst 2017-4-21

ellipse_rotated.m

See attached demo.

请先登录，再进行评论。

Answer 2

Roger Stafford 2017-3-13

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/329193-how-to-find-the-end-of-major-and-minor-axis-of-an-ellipsoid#answer_258442

在 MATLAB Online 中打开

I think you need

axis equal

so that scaling is the same for both axes.

1 个评论
显示 -1更早的评论隐藏 -1更早的评论

nadia nadi 2017-3-13

编辑：nadia nadi 2017-3-13

Sorry I did it but it does not work. Best,

请先登录，再进行评论。

Answer 3

Roger Stafford 2017-4-21

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/329193-how-to-find-the-end-of-major-and-minor-axis-of-an-ellipsoid#answer_263938

编辑：Walter Roberson 2017-4-21

在 MATLAB Online 中打开

I will make some assumptions about the ellipse you describe:

The ‘a’ and ‘b’ values are the lengths of the ellipse’s semi-major and semi-minor axes, respectively.
xC and yC are the cartesian coordinates of the ellipse’s center.
The ‘angle’ is the angle in degrees, measured counterclockwise, from the x-axis to the ellipse major axis.

The ellipse axes’ four ends will then be:

Major axis, upper right: x1 = xC+a*cosd(angle)
                         y1 = yC+a*sind(angle)
            lower left:  x2 = xC-a*cosd(angle)
                         y2 = yC-a*sind(angle)
Minor axis, upper left:  x3 = xC-b*sind(angle)
                         y3 = yC+b*cosd(angle)
            lower right: x4 = xC+b*sind(angle)
                         y4 = yC-b*cosd(angle)

You can make a plot of the ellipse as:

   t = linspace(-180,180,1000);
   x = xC+a*cosd(t)*cosd(angle)-b*sind(t)*sind(angle);
   y = yC+a*cosd(t)*sind(angle)+b*sind(t)*cosd(angle);
   plot(x,y,’y-‘,[x1,x2],[y1,y2],’r*’,[x3,x4],[y3,y4],’g*’)
   axis equal