placematrix

 function m1 = placematrix(m1,m2,pos)

 <m1> is a 2D matrix, with potentially some extra stuff in the third dimension.
 <m2> is a 2D matrix, with potentially some extra stuff in the third dimension.
   note that size(m1,3) must equal size(m2,3).
 <pos> (optional) is [R C] with a position.  R and C can be any integers.
   special case is [] which means to center <m2> with respect to <m1>.
   if exact centering can't be achieved, we shift down and right.
   default: [].

 place <m2> in <m1> positioned with first element at <pos>.
 if any part of <m2> lies outside of <m1>, it just gets ignored.

 example:
 isequal(placematrix([1 2 3; 4 5 6; 7 8 9],[10 10; 10 10],[0 0]),[10 2 3; 4 5 6; 7 8 9])

0001 function m1 = placematrix(m1,m2,pos)
0002 
0003 % function m1 = placematrix(m1,m2,pos)
0004 %
0005 % <m1> is a 2D matrix, with potentially some extra stuff in the third dimension.
0006 % <m2> is a 2D matrix, with potentially some extra stuff in the third dimension.
0007 %   note that size(m1,3) must equal size(m2,3).
0008 % <pos> (optional) is [R C] with a position.  R and C can be any integers.
0009 %   special case is [] which means to center <m2> with respect to <m1>.
0010 %   if exact centering can't be achieved, we shift down and right.
0011 %   default: [].
0012 %
0013 % place <m2> in <m1> positioned with first element at <pos>.
0014 % if any part of <m2> lies outside of <m1>, it just gets ignored.
0015 %
0016 % example:
0017 % isequal(placematrix([1 2 3; 4 5 6; 7 8 9],[10 10; 10 10],[0 0]),[10 2 3; 4 5 6; 7 8 9])
0018 
0019 %% SEE ALSO padarray.m ?
0020 %% see also assignsubvolume2.m???
0021 
0022 % input
0023 if ~exist('pos','var') || isempty(pos)
0024   pos = [];
0025 end
0026 
0027 m1r = size(m1,1);
0028 m1c = size(m1,2);
0029 m2r = size(m2,1);
0030 m2c = size(m2,2);
0031 
0032 if isempty(pos)
0033   pos = [1+ceil((m1r-m2r)/2) 1+ceil((m1c-m2c)/2)];
0034 end
0035 
0036 badup = max(0,1-pos(1));               % how many bad pixels to the up
0037 badleft = max(0,1-pos(2));             % how many bad pixels to the left
0038 baddown = max(0,(pos(1)+m2r-1)-m1r);   % how many bad pixels to the bottom
0039 badright = max(0,(pos(2)+m2c-1)-m1c);  % how many bad pixels to the right
0040 
0041 m1(pos(1)+badup:pos(1)+m2r-1-baddown,pos(2)+badleft:pos(2)+m2c-1-badright,:) = ...
0042   m2(1+badup:end-baddown,1+badleft:end-badright,:);