Rotating a partial section of a circle around its center

Halo all,

I am trying to develop a program with the following aim.

** A partial section** of a circle which rotates around its center with constant angular velocity.


A circle with radius 150 mm (center located at 0,0) is equipped with known points along its circumference as shown in Figure below. A partial section (with constant length) should be identified and observed as it moves around the circle. With the below mentioned code (written in FORTRAN) i am able to locate two points (point A and B) as they move with time but not able to capture points lying between these two points (A and B). Please check the code below. Thank you in advance.

c calculate the new position
c measure the Difference to the Center
difx1 = PointAx - originx
dify1 = PointAy - originy

     difx2  = PointBx - originx
     dify2  = PointBy - originy

c calculate the angle in RADIANs
c Theta = w * time w is angular velocity in rad/sec
radns = angvel * time

     newx   = cos(radns)
     newy   = sin(radns)

     dx1    = (difx1 * newx) - (dify1 * newy)
     dx2    = (difx2 * newx) - (dify2 * newy)

     dy1    = (difx1 * newy) + (dify1 * newx)
     dy2    = (difx2 * newy) + (dify2 * newx)

     PointAx  = originx + dx1
     PointAy  = originy + dy1

     PointBx  = originx + dx2
     PointBy  = originy + dy2

c check weather this node LIES in the heating Zone ** [COLOR=Red]/ HERE IS PROBLEM, How to locate region between two points A and B[/COLOR]**
if((points(1) .lt. PointBx) .or. (points(1) .gt. PointAx)) then

c NOT in the region
c DO Not apply anything

     xin = .true.
  end if

c [COLOR=Red]/ HERE IS PROBLEM, How to locate region between two points A and B[/COLOR]
if((points(2) .lt. PointAy) .or. (points(2) .gt. PointB)) then

C Not in the region
C DO Not apply anything

     yin = .true.
  end if

    IF (xin .and. yin) then

c WE are in the Region

 end if 

I just wanted to get the region between the two nodes. Thank you.