set path [get3DEInstallPath]
source $path/user_data/tcl_archive/veclib.tcl

proc getBackProjectedPoint2D { pg point fobj frame }\
	{
	set pg_type [getPGroupType $pg]
	set cam [getFobjCamera $fobj]

	# Geomery of the Camera
	set focal [getCameraFocalLength $cam]
	set width [getCameraFBackWidth $cam]
	set height [getCameraFBackHeight $cam]
	# Lens center offset
	set lcx [getCameraLensCenterX $cam]
	set lcy [getCameraLensCenterY $cam]

	# Field of View size in pixel
	set fov_width [getFobjImageWidthFOV $fobj]
	set fov_height [getFobjImageHeightFOV $fobj]

	set x [getPointCalcPosition3D $pg $point]
	
	set pos [getPGroupPosition3D $pg $fobj $frame]
	set rot [getPGroupRotation3D $pg $fobj $frame]
	
	if {$pg_type == "CAMERA"}\
		{
		# Difference vector from the camera position to the point in 3d
		set d [vec3-vec3 $x $pos]
		# Calculate the inverse of the camera matrix
		set rotinv [mat3trans $rot]
		# Reformulate the Difference vector in the coordiante frame of the camera
		set dnew [mat3*vec3 $rotinv $d]
		# Project this into the z=-1-Plane, that is: x' = x / -z, y' = y' -z (remember: the camera looks into -z direction)
		set d2 [vec2/s [list [vget $dnew 0] [vget $dnew 1]] [expr -[vget $dnew 2]]]
		# Now we want to express this in pixel respective to the lower left corner of the field of view (dotted line)
		# We scale it to metric units, remove the lens center offset, scale it down to dimensionless coordinates,
		# so that (0,0) is the lower left corner of the field of view, and (1,1) is the lower upper corner.
		set dfovx [expr ([vget $d2 0] * $focal - $lcx) / ($width) + .5]
		set dfovy [expr ([vget $d2 1] * $focal - $lcy) / ($height) + .5]
		}

	# This doesn't work yet:
	if {$pg_type == "OBJECT"}\
		{
		set rotinv [mat3invert $rot]
		set d [mat3*vec3 $rotinv $x]
		set dnew [vec3+vec3 $d $pos]
		set d2 [vec2/s [list [vget $dnew 0] [vget $dnew 1]] [expr -[vget $dnew 2]]]
		set dfovx [expr ([vget $d2 0] * $focal - $lcx) / ($width) + .5]
		set dfovy [expr ([vget $d2 1] * $focal - $lcy) / ($height) + .5]
		}
			
	set pos2d [list $dfovx $dfovy]
	
	return $pos2d
	}
		

set fobj [getSelectedFobj]
if {$fobj==0}\
        {
                bell
                post3DEInfoRequester "Error, there is no sequence selected!"
                return
        }

set pg [getSelectedPGroup]
if {$pg==0}\
        {
                bell
                post3DEInfoRequester "Error, there is no point group selected!"
                return
        }

set width [getFobjImageWidth $fobj]
set height [getFobjImageHeight $fobj]
set no_frames [getFobjNoFrames $fobj]

set string [post3DEPromptRequester "Enter Framerange (<startframe> <endframe>):"]
set start [lindex $string 0]
set end [lindex $string 1]

for {set point [getFirstPoint $pg]} {$point!=0} {set point [getNextPoint $pg $point]}\
	{
	set selected [getPointSelectionFlag $pg $point]
	if {$selected}\
		{
		set curve [getPointPosition2DBlock $pg $point $fobj 1 $no_frames]
		for {set frame $start} {$frame<=$end} {set frame [expr $frame+1]}\
			{
			set pos2d [getBackProjectedPoint2D $pg $point $fobj $frame]
			set curve [lreplace $curve [expr $frame-1] [expr $frame-1] $pos2d]
			}
		setPointPosition2DBlock $pg $point $fobj 1 $curve
		}
	}