知道 Matlab 中的给定点在哪个区域

Question

Given a1x + b1y + c1 =0 the line AB a2 x + b2y + c2=0 and the line CD

how would one write a program to know in which zone is a given point (the lines intersect making an X shape)

Answer 1

Fill in the value for x and y of a given point, so if point is (1,2):

a1 x 1 + b1 x 2 + c1

• If this is > 0, than the point is above line 1
• If this is < 0, than the point is below line 1
• If this is ==0, than the point is on line 1

Same goes for line 2

a2 x 1 + b2 x 2 + c2

• If this is > 0, than the point is above line 2
• If this is < 0, than the point is below line 2
• If this is ==0, than the point is on line 2

And then you can combine both results and know where your point is