assign2points

 PURPOSE: assign to a set of points the values sampled at an underlying
          raster
 -------------------------------------------------------------------------
 USAGE: P = assign2points(PS,raster,xcoords,ycoords);
 where: [PS] is the set of points as an array in the form [xcoord, ycoord]         
        [raster] is the raster to be sampled%        
        [xcoords],[ycoords] are coordinate vectors of the raster
        [delNaN] (optional) flag to delete all points with NaN in
                 valuefield. 1= delete NaNs; 0= leave NaNs in pointset.
 -------------------------------------------------------------------------
 OUTPUTS:
        [P] is the original point set with an additional third column
        holding values of the raster sampled at the coordinates. The output 
        array has the form [xcoord, ycoord, value]
 -------------------------------------------------------------------------
 NOTES: ycoords(1) and xcoords(1) should have the llc coords of raster.
        if target coord lies exactely on the border of two cells, 
        lower left cell is sampled.
        

 See also:  sample_center()

 Felix Hebeler, Geography Dept., University Zurich, April 2006.

0001 function PS = assign2points(PS,raster,xcoords,ycoords,delNaN)
0002 % PURPOSE: assign to a set of points the values sampled at an underlying
0003 %          raster
0004 % -------------------------------------------------------------------------
0005 % USAGE: P = assign2points(PS,raster,xcoords,ycoords);
0006 % where: [PS] is the set of points as an array in the form [xcoord, ycoord]
0007 %        [raster] is the raster to be sampled%
0008 %        [xcoords],[ycoords] are coordinate vectors of the raster
0009 %        [delNaN] (optional) flag to delete all points with NaN in
0010 %                 valuefield. 1= delete NaNs; 0= leave NaNs in pointset.
0011 % -------------------------------------------------------------------------
0012 % OUTPUTS:
0013 %        [P] is the original point set with an additional third column
0014 %        holding values of the raster sampled at the coordinates. The output
0015 %        array has the form [xcoord, ycoord, value]
0016 % -------------------------------------------------------------------------
0017 % NOTES: ycoords(1) and xcoords(1) should have the llc coords of raster.
0018 %        if target coord lies exactely on the border of two cells,
0019 %        lower left cell is sampled.
0020 %
0021 %
0022 % See also:  sample_center()
0023 %
0024 % Felix Hebeler, Geography Dept., University Zurich, April 2006.
0025 
0026 PS(:,3)=NaN;
0027 for i=1:size(PS,1)
0028     PS(i,3)=s_c(PS(i,1),PS(i,2),xcoords,ycoords,raster);
0029 end
0030 
0031 % awkward way to delete NaNs... its getting late...
0032 if exist('delNaN','var')
0033     if delNaN==1;
0034        i=1;
0035        while i<size(PS,1)
0036             if isnan(PS(i,3))
0037                 PS(i,:)=[];
0038             else
0039                 i=i+1;
0040             end
0041        end          
0042     end
0043 end
0044 
0045 
0046 function value = s_c(sx,sy,xcoord,ycoord,grid)
0047 % the sample_center function
0048 % calculate source cellsize
0049 xcs= abs(xcoord(2)-xcoord(1)); ycs= abs(ycoord(2)-ycoord(1));
0050 
0051 % get distance on x and y axis
0052 dx=abs(xcoord(1)- sx);
0053 dy=abs(ycoord(1)- sy);
0054 if sx>max(xcoord) || sy>max(ycoord) || sx<min(xcoord) || sy<min(ycoord)
0055     value = NaN;
0056     return
0057 end
0058 value = grid(size(raster,1)-(floor(dy/ycs)+1)+1, (floor(dx/xcs)+1));