I'm confused, every line thru 2 points is straight.

Actually you are calculating with 3 points P, P1 and P2 with P=($x,$y)

Is your intention to check if the path P1-P2 and P-P1 are on the same straight line or what?

One approach:

A path is "straight" iff the two vectors are identical after normalization (i.e. shortened to length 1 and with same orientation)

To normalize them divide each component by the length of the vector.

In 2 dimensional space you get the length simply by applying Pythagoras...in higher dimension use the scalar product.

Another (easier)approach:

Calculate the normal vector n of P1-P2 (a normalized vector orthogonal to the line).

The scalar product (aka dot product) of n · (P-P1) == 0 iff P,P1 and P2 are collinear.

Don't wanna go deeper into details thats all school stuff...

Cheers Rolf

In reply to Re: Check if line is straight by LanX
in thread Check if line is straight by Anonymous Monk

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