Find which side of a line is my point

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Clementine Bodin
Clementine Bodin 2022-12-12
评论： Clementine Bodin 2022-12-12
Hello ,
I'm looking for a simple way to know where C or D are in relation to the line AB
I already computed their distance to line AB but it is absolute so I don't know in which direction they are.
Would someone have a solution for this ? Ideally to obtain a negative distance for point C and positive one for point D
I tried computing coeff d=(x−x1)(y2−y1)−(y−y1)(x2−x1) but it's not working well
Thanks a lot

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Bora Eryilmaz
Bora Eryilmaz 2022-12-12
编辑：Bora Eryilmaz 2022-12-12
Ran in:
You can use the sign of the z-term of the cross product of the vectors defining the line and the points of interest:
vAB = [3 2 0]; % Vector from A to B, or anywhere along the line
vC = [5 2 0]; % From origin to C
vD = [2 4 0]; % From origin to D
X = cross(vAB, vC);
sign(X(3)) % Below the line when negative
ans = -1
Y = cross(vAB, vD);
sign(Y(3)) % Above the line when positive
ans = 1
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Bora Eryilmaz
Bora Eryilmaz 2022-12-12
编辑：Bora Eryilmaz 2022-12-12
vAb = [xb-xa, yb-ya, 0]
vC = [xc, yc, 0]
You don't need the point of intersection. You need the coordinates of C and D.
Clementine Bodin
Clementine Bodin 2022-12-12
Ok got it it seems to work now !! thank you so much

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