C+
C NAME:
C	smei_skyd_checkpix
C PURPOSE:
C	Check location of pixel against reference camera frame
C	defining a great circle on the sky defining at the seam
C	between start and end of orbit
C CATEGORY:
C	camera/for/sky
C CALLING SEQUENCE:
	logical function smei_skyd_checkpix(pfov,runit,qq_cam2cam_edge)
C INPUTS:
C	pfov		integer	linear array index into CCD frame
C	runit(*)	double precision
C				unit vector in current camera frame
C	qq_cam2cam_edge(*)
C			double precision
C				quaternion that rotates vectors from
C				current camera frame to reference frame
C OUTPUTS:
C	smei_skyd_checkpix
C			logical see Procedure
C CALLS:
C	quaternion_rotate_xyz
C PROCEDURE:
C	The camera frame has z-axis along the optical axis, x-axis
C	along the long dimension of the fov, and y-axis along the
C	narrow dimension such that y increases with decreasing radius
C	on the CCD. Stars travel in the direction of decreasing y;
C	frames sweep the sky in the direction of increasing y.
C
C	The reference camera frame is defined by the nominal viewing
C	direction of camera 2 at the start of an orbit. The long
C	dimension of camera 2 defines a reference circle that is used
C	separate start and end of orbit.
C
C	If a pixel in any frame near start or end of the orbit has
C	a negative y than it is traveling towards the reference
C	circle; if it has positive y it is traveling away from it.
C
C	For frames near the start of an orbit negative y
C	(smei_skyd_checkpix=.FALSE.) means the pixel is part of the
C	previous orbit; positive y (smei_skyd_checkpix=.TRUE.)
C	means the pixel is part of the current orbit.
C
C	For frames near the end of an orbit negative y
C	(smei_skyd_checkpix=.FALSE.) means the pixel is still in the
C	current orbit; positive y (smei_skyd_checkpix=.TRUE.)
C	means the pixel is part of the next orbit.
C MODIFICATION HISTORY:
C	OCT-2006, Paul Hick (UCSD/CASS; pphick@ucsd.edu)
C-
	    integer		pfov
	    double precision	runit(*)
	    double precision	qq_cam2cam_edge(*)

	double precision rx
	double precision ry
	double precision rz

	! Unit vector in camera frame

	rx = runit(1)
	ry = runit(2)
	rz = runit(3)

	!dval = dsqrt(rx*rx+ry*ry+rz*rz)
	!rx = rx/dval
	!ry = ry/dval
	!rz = rz/dval

	! Rotate to camera 2 frame at start of orbit.

	call quaternion_rotate_xyz(qq_cam2cam_edge,rx,ry,rz)

	smei_skyd_checkpix = ry .ge. 0.0d0

	return
	end