# How can i calculate that normal lays in same part of plane with point?

I.e. n0 for A and n1 for B. Plane divided by plane CD.

First, find the center:

p0 = (C + D) * 0.5


Now, take the relative vector from the center to the point in question:

p1 = (X - p0)


Finally, take the dot product with the normals you might want:

d0 = n0.dot(p1)
d1 = n1.dot(p1)
...
etc.


Then, check to see if its greater than zero

abovePlane0 = d0 > 0
abovePlane1 = d1 > 0


... etc.

• Is p0 = (C + D) * 0.5 the same, as just coordinates of vector CD D-C – Alex.M Feb 26 '15 at 17:38
• No. (C + D) * 0.5 is the midpoint between C and D. – mklingen Feb 26 '15 at 17:39
• And X - my point of interest ? – Alex.M Feb 26 '15 at 17:41
• X, meaning A, B, etc. the point you want to check. – mklingen Feb 26 '15 at 17:42
• I believe finding midpoint is superfluous. Knowing just two vectors (n and CA) dot product can be found and its sign checked for being smaller or greater than zero. – Kromster says support Monica Feb 27 '15 at 15:39