function [VarianceIn3D, ArrResiduals] = VarOfBackProjectTraj( TrajByFrame, offsetForFrameNums, Kbig, Rbig, Tbig )

iBegin = 1;
iEnd = size(TrajByFrame,1);
iCentral = ceil( iEnd / 2);


% % --------Shortcut------------
% frameNumCentral = TrajByFrame(iCentral, 1);
% iInBig = frameNumCentral - offsetForFrameNums;
% Pa = Kbig(:,:, iInBig ) * Rbig(:,:, iInBig ) * [eye(3) -Tbig(:,:, iInBig )];
% xa = TrajByFrame(iCentral, 2:3)';
% 
% frameNumCur = TrajByFrame(iBegin, 1);
% iInBig = frameNumCur - offsetForFrameNums;
% Pb = Kbig(:,:, iInBig ) * Rbig(:,:, iInBig ) * [eye(3) -Tbig(:,:, iInBig )];
% xb = TrajByFrame(iBegin, 2:3)';
% [X1, res1] = BackProject2UVsBy2Projs( xa, xb, Pa, Pb );
% %[WorldCoord, residual] = BackProject2UVsBy2Projs( xa, xb, Pa, Pb );
% 
% frameNumCur = TrajByFrame(iEnd, 1);
% iInBig = frameNumCur - offsetForFrameNums;
% Pb = Kbig(:,:, iInBig ) * Rbig(:,:, iInBig ) * [eye(3) -Tbig(:,:, iInBig )];
% xb = TrajByFrame(iEnd, 2:3)';
% [X2, res2] = BackProject2UVsBy2Projs( xa, xb, Pa, Pb );
% 
% %VarianceIn3D = X1-X2; ArrResiduals = norm([res1 res2]);
% %VarianceIn3D = det(cov(X1-X2)); ArrResiduals = norm([res1 res2]);
% 
% VarianceIn3D = X1-X2;       % V01, then norm'd
% % xBeg = Pa*[X1;1]; xBeg = xBeg / xBeg(3);
% % xEnd = Pa*[X2;1]; xEnd = xEnd / xEnd(3);
% % ArrResiduals = norm(    var([xBeg(1:2) xa xEnd(1:2)]')     );   % V02
% 
% ArrResiduals = norm([res1 res2]); % V03
% return; % V01 V02 V03
% %---------Endof shortcut------------

ArrWorldPts = zeros( size(TrajByFrame,1) -1, 3);
ArrResiduals = zeros( size(TrajByFrame,1) -1, 4);
indexArrWorldPts = 1;

frameNumCentral = TrajByFrame(iCentral, 1);
iInBig = frameNumCentral - offsetForFrameNums;

Pa = Kbig(:,:, iInBig ) * Rbig(:,:, iInBig ) * [eye(3) -Tbig(:,:, iInBig )];
xa = TrajByFrame(iCentral, 2:3)';
for( iFrame = iBegin:iEnd )
    if( iFrame == iCentral )
        continue; % Skip it, since we can't triangulate against same frame.
    end;

    frameNumCur = TrajByFrame(iFrame, 1);
    iInBig = frameNumCur - offsetForFrameNums;
    Pb = Kbig(:,:, iInBig ) * Rbig(:,:, iInBig ) * [eye(3) -Tbig(:,:, iInBig )];
    xb = TrajByFrame(iFrame, 2:3)';

    [WorldCoord, residual] = BackProject2UVsBy2Projs( xa, xb, Pa, Pb );
    ArrWorldPts( indexArrWorldPts, 1:3 ) = WorldCoord';
    ArrResiduals( indexArrWorldPts, 1:4 ) = residual';
    indexArrWorldPts = indexArrWorldPts +1;
end;


VarianceIn3D = var(ArrWorldPts);
ArrResiduals = norm(var(ArrResiduals));   %V04
%VarianceIn3D = det(cov(ArrWorldPts));

% numPts = size(ArrWorldPts,1);
% VarianceIn3D = sum(abs(ArrWorldPts(1:numPts-1, :) - ArrWorldPts(2:numPts, : )) ) / (numPts-1) ; %V05