polygon boundries checking

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hi in this code why if distance<=1 we say that the point(xI,yI)is in bound?
thank you

C#

if (IsInLineBound(seg1, xI, yI) && IsInLineBound(seg2, xI, yI))
           {
               double distance1 = Math.Sqrt(Math.Pow((seg1.p.X - xI), 2.0) + Math.Pow((seg1.p.Y - yI), 2.0));
               double distance2 = Math.Sqrt(Math.Pow((seg1.q.X - xI), 2.0) + Math.Pow((seg1.q.Y - yI), 2.0));

               if (distance1 <= 1 || distance2 <= 1)
               {
                   return false;
               }
               else
               {
                   return true;
               }
           }
           else
           {
               return false;
           }
       }

       private bool IsInLineBound(Segment seg, double xI, double yI)
       {
           bool xI_OK = false;
           bool yI_OK = false;
           // x bound check
           if (seg.p.X > seg.q.X)
           {
               if (xI > seg.q.X && xI < seg.p.X)
               {
                   xI_OK = true;
               }
               else
               {
                   return false;
               }
           }
           else if (seg.p.X < seg.q.X)
           {
               if (xI > seg.p.X && xI < seg.q.X)
               {
                   xI_OK = true;
               }
               else
               {
                   return false;
               }
           }
           else if (seg.p.X == seg.q.X)
           {
               if (xI == seg.p.X)
               {
                   xI_OK = true;
               }
               else
               {
                   return false;
               }
           }

           // y bound check
           if (seg.p.Y > seg.q.Y)
           {
               if (yI > seg.q.Y && yI < seg.p.Y)
               {
                   yI_OK = true;
               }
               else
               {
                   return false;
               }
           }
           else if (seg.p.Y < seg.q.Y)
           {
               if (yI > seg.p.Y && yI < seg.q.Y)
               {
                   yI_OK = true;
               }
               else
               {
                   return false;
               }
           }
           else if (seg.p.Y == seg.q.Y)
           {
               if (yI == seg.p.Y)
               {
                   yI_OK = true;
               }
               else
               {
                   return false;
               }
           }

           if (xI_OK && yI_OK)
               return true;
           return false;
       }

Posted 22-Dec-11 5:47am

minooshi

Updated 22-Dec-11 5:48am

Wendelius

v2

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#realJSOP · Answer 1 · 2011-12-22T05:53:00

Solution 1

How are we supposed to know? You didn't post enough of the code for us to determine that (and no, you don't have to post any more code). Why don't you run it under the debugger and try to find out why it's doing what it's doing?

Posted 22-Dec-11 5:53am

#realJSOP

Comments

minooshi 22-Dec-11 11:59am

private bool IsIntersected(Segment seg1 ,Segment seg2)
{
double xI, yI;
double a1, a2, b1, b2;

if (((seg1.p.X - seg1.q.X) == (seg2.p.X - seg2.q.X)) && (seg2.p.X - seg2.q.X) == 0)
{
// parallel lines
return false;
}
if ((seg1.p.X - seg1.q.X) == 0)
{
a2 = (double)(seg2.p.Y - seg2.q.Y) / (double)(seg2.p.X - seg2.q.X);
b2 = (double)seg2.p.Y - (a2 * seg2.p.X);

xI = seg1.p.X;
yI = a2 * xI + b2;
}
else if ((seg2.p.X - seg2.q.X) == 0)
{
a1 = (double)(seg1.p.Y - seg1.q.Y) / (double)(seg1.p.X - seg1.q.X);
b1 = (double)seg1.p.Y - (a1 * seg1.p.X);

xI = seg2.p.X;
yI = a1 * xI + b1;
}
else
{
a1 = (double)(seg1.p.Y - seg1.q.Y) / (double)(seg1.p.X - seg1.q.X);
a2 = (double)(seg2.p.Y - seg2.q.Y) / (double)(seg2.p.X - seg2.q.X);

b1 = (double)seg1.p.Y - (a1 * seg1.p.X);
b2 = (double)seg2.p.Y - (a2 * seg2.p.X);

// two lines are parallel and there is no intersection
if (a1 == a2)
{
return false;
}
else
{
xI = (b2 - b1) / (a1 - a2);
yI = (a1 * xI) + b1;
}
}

// intersection on line bound checking
if (IsInLineBound(seg1, xI, yI) && IsInLineBound(seg2, xI, yI))
{
double distance1 = Math.Sqrt(Math.Pow((seg1.p.X - xI), 2.0) + Math.Pow((seg1.p.Y - yI), 2.0));
double distance2 = Math.Sqrt(Math.Pow((seg1.q.X - xI), 2.0) + Math.Pow((seg1.q.Y - yI), 2.0));

if (distance1 <= 1 || distance2 <= 1)
{
return false;
}
else
{
return true;
}
}
else
{
return false;
}
}

private bool IsInLineBound(Segment seg, double xI, double yI)
{
bool xI_OK = false;
bool yI_OK = false;
// x bound check
if (seg.p.X > seg.q.X)
{
if (xI > seg.q.X && xI < seg.p.X)
{
xI_OK = true;
}
else
{
return false;
}
}
else if (seg.p.X < seg.q.X)
{
if (xI > seg.p.X && xI < seg.q.X)
{
xI_OK = true;
}
else
{
return false;
}
}
else if (seg.p.X == seg.q.X)
{
if (xI == seg.p.X)
{
xI_OK = true;
}
else
{
return false;
}
}

// y bound check
if (seg.p.Y > seg.q.Y)
{
if (yI > seg.q.Y && yI < seg.p.Y)
{
yI_OK = true;
}
else
{
return false;
}
}
else if (seg.p.Y < seg.q.Y)
{
if (yI > seg.p.Y && yI < seg.q.Y)
{
yI_OK = true;
}
else
{
return false;
}
}
else if (seg.p.Y == seg.q.Y)
{
if (yI == seg.p.Y)
{
yI_OK = true;
}
else
{