MATLAB: How to draw a perpendicular to a line from a point

perpendicular

I need to draw a perpendicular line from a point (x1,y1) to a line. How to do that?

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I showed you how to plot a line starting with any point and for any angle and length of line in How to draw a tangent using a point and an angle? (link).

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MATLAB: How to draw a perpendicular line

The slope of a line perpendicular to another has a slope that is -1 over the slope of the other line. so

coefficients = polyfit(xKnown, yKnown, 1);
slope = coefficients(1);

Now get the min and max x where you want to draw the line.

[x1p, index1] = min(xKnown);
[x2p, index2] = max(xKnown);
% Get y at those endpoints
y1p = yKnown(index1);
y2p = yKnown(index2);
% Compute the slope
perpSlope = -1 / slope;
% Equation of line going through the left most x (at x1p) is
% (y - y1p) = perpSlope * (x - x1p)
y1 = perpSlope * (x1p - xKnown(index1)) + y1p
y2 = perpSlope * (x2p - xKnown(index1)) + y1p
line([x1p, x2p], [y1, y2], 'Color', 'r')

It's untested code, so no guarantees.

MATLAB: Why cant i rotate the 2nd line at the X axis it takes reference as point 0,0 and rotates at 45 degree angle i want to rotate the line at same axis

It is rotating. Look at the top of your plot.

The way to rotate relative to a point is to subtract the coordinates of the point to rotate around, do the rotation, then add the coordinates of the point to rotate around back in. If you want ot rotate around (800,0) then cart2pol(x1-800,y1) and plot(x1r+800,y1r)

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MATLAB: How to draw a perpendicular line

MATLAB: Why cant i rotate the 2nd line at the X axis it takes reference as point 0,0 and rotates at 45 degree angle i want to rotate the line at same axis

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