Question

If I have an array of points (x,y,z) and am given a single point (x,y,z), what code do I use to determine if that point resides within the shape defined by the array?

I am drawing a blank on this one…

I’m using C#

EDIT

Thanks for the responses guys, from the comments I have found this link (http://alienryderflex.com/polygon/) which explains the process quite well.

Thanks!

FYI:

bool pointInPolygon() {
    
      int      i, j=polySides-1 ;
      boolean  oddNodes=NO      ;
    
      for (i=0; i<polySides; i++) {
        if (polyY[i]<y && polyY[j]>=y
        ||  polyY[j]<y && polyY[i]>=y) {
          if (polyX[i]+(y-polyY[i])/(polyY[j]-polyY[i])*(polyX[j]-polyX[i])<x) {
            oddNodes=!oddNodes; }}
        j=i; }
     
      return oddNodes; }

It’ll need some work, but thats the guts of it.

Thanks again

Answer 1

Use a point that you know is outside the shape, and check if the line from that point to the given point passes through the surfaces of the shape. If it passes through an odd number of surfaces, the given point is inside the shape.