function [XYin3D] = BackProject2DTrajTo3D( TrajByFrame, offsetForFrameNums, Kbig, Rbig, Tbig )
% Use first and last known 2D locations of this Traj to compute 3D with
% greatest disparity.

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

frameNumCur = TrajByFrame(iBegin, 1);
iInBig = frameNumCur - offsetForFrameNums;
Pa = Kbig(:,:, iInBig ) * Rbig(:,:, iInBig ) * [eye(3) -Tbig(:,:, iInBig )];
xa = TrajByFrame(iBegin, 2:3)';

frameNumCur = TrajByFrame(iEnd, 1);
iInBig = frameNumCur - offsetForFrameNums;
Pb = Kbig(:,:, iInBig ) * Rbig(:,:, iInBig ) * [eye(3) -Tbig(:,:, iInBig )];
xb = TrajByFrame(iEnd, 2:3)';
[XYin3D, res] = BackProject2UVsBy2Projs( xa, xb, Pa, Pb );

return;