MATLAB: How to draw a tangent using a point and an angle

tangent

I need to draw a tangent from (0,0) with an angle of 89.8412 as shown in the curve. How to do that?

Best Answer

Try this:

ad = 89.8412;                                           % Angle (Degrees)
tangline = 200*[0 cosd(ad); 0 sind(ad)];
figure
plot(tangline(1,:), tangline(2,:))
grid
axis([0  2    0  300])

It produces two vectors in the ‘tangline’ matrix, the first row being the x-coordinates and the second row the y-coordinates. It then plots them.

You can check that these are correct with:

Check = atan2d(diff(tangline(2,:)), diff(tangline(1,:)))

It returns the ‘ad’ value.

Related Solutions

MATLAB: Does the array only work once

Use element-wise division:

Phi = asind(AB*sind(Theta)./AD);
                          ↑ ← HERE

and:

P = Mb./(BD*sind(90 - Phi));
      ↑ ← HERE

and element-wide multiplication:

Ma = P .* AD;
       ↑ ← HERE

and the calculations do what you want them to do.

MATLAB: How to find the coordinates of the point of intersection of a line and a curve

Add these lines to the end of the previous code (How to draw a tangent using a point and an angle?):

x2_near_origin_idx = find(x2 <= origin(1), 1, 'last');
B2 = [x2(x2_near_origin_idx) 1; x2(x2_near_origin_idx+1) 1] \ [y2(x2_near_origin_idx); y2(x2_near_origin_idx+1)];   % Equation Of Data Near ‘tangline’

Btl = [tangline(1,1) 1; tangline(1,2) 1] \ [tangline(2,1); tangline(2,2)];                                          % Equation Of ‘tangline’

xint = -(B2(2) - Btl(2)) / (B2(1) - Btl(1));
yint = [xint 1] * B2;
plot(xint, yint, '+r')

so the entire code is now:

filename1 = 'finalocc.xlsx';
filename2 = 'Nzpftest.xlsx';
values1 = xlsread(filename2,'Sheet1','A1:B7');
x1 = values1(:,1);
y1 = values1(:,2);
plot(y1,x1)
hold on
values2 = xlsread(filename1,'Sheet1','A2:B14');
x2 = values2(:,1);
y2 = values2(:,2);
plot(x2,y2, '.-')
dist= 0.32;
xx=interp1(y2,x2,50)
m=(50-0)/(xx-0);
deg= atand(m)
plot([1.68,2],[240.177,240.177])
% hold on
ad = 89.8412;                                         
origin = [1.68;240.177];
lineLen = 20;
tangline = [0 cosd(ad);0 sind(ad)];
tangline = bsxfun(@plus, lineLen*[0 cosd(ad);0 sind(ad)], origin);
plot(tangline(1,:), tangline(2,:))
x2_near_origin_idx = find(x2 <= origin(1), 1, 'last');
B2 = [x2(x2_near_origin_idx) 1; x2(x2_near_origin_idx+1) 1] \ [y2(x2_near_origin_idx); y2(x2_near_origin_idx+1)];   % Equation Of Data Near ‘tangline’
Btl = [tangline(1,1) 1; tangline(1,2) 1] \ [tangline(2,1); tangline(2,2)];                                          % Equation Of ‘tangline’
xint = -(B2(2) - Btl(2)) / (B2(1) - Btl(1));
yint = [xint 1] * B2;
plot(xint, yint, '+r')
hold off

The point of intersection will be plotted as a red ‘+’ at (xint,yint).

Best Answer

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MATLAB: Does the array only work once

MATLAB: How to find the coordinates of the point of intersection of a line and a curve

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