som_vis_coords

Syntax

  Co = som_vis_coords(lattice, msize)

Description

 This function calculates the coordinates of map units in 'hexa' and
 'rect' lattices in 'sheet' shaped map for visualization purposes. It
 differs from SOM_UNIT_COORDS in the sense that hexagonal lattice is
 calculated in a "wrong" way in order to get integer coordinates for
 the units. Another difference is that it may be used to calculate
 the coordinates of units _and_ the center points of the lines
 connecting them (edges) by using 'hexaU' or 'rectU' for lattice. 
 This property may be used for drawing u-matrices.

 The unit number 1 is set to (ij) coordinates (1,1)+shift
                 2                            (2,1)+shift

  ... columnwise

             n-1th                        (n1-1,n2)+shift
             nth                            (n1,n2)+shift

 where grid size = [n1 n2] and shift is zero, except for 
 the even lines of 'hexa' lattice, for which it is +0.5.

 For 'rectU' and 'hexaU' the unit coordinates are the same and the
 coordinates for connections are set according to these. In this case
 the ordering of the coordinates is the following:
   let
     U  = som_umat(sMap); U=U(:); % make U a column vector
     Uc = som_vis_coords(sMap.topol.lattice, sMap.topol.msize); 
   now the kth row of matrix Uc, i.e. Uc(k,:), contains the coordinates 
   for value U(k). 

Required input arguments

  lattice  (string) The local topology of the units: 
                    'hexa', 'rect', 'hexaU' or 'rectU'
  msize    (vector) size 1x2, defining the map grid size. 
                    Notice that only 2-dimensional grids
                    are allowed.

Output arguments

  Co       (matrix) size Mx2, giving the coordinates for each unit.
                    M=prod(msize) for 'hexa' and 'rect', and 
                    M=(2*msize(1)-1)*(2*msize(2)-1) for 'hexaU' and 'rectU'

Features

 Only 'sheet' shaped maps are considered. If coordinates for 'toroid'
 or 'cyl' topologies are required, you must use SOM_UNIT_COORDS
 instead.

Examples

 Though this is mainly a subroutine for visualizations it may be
 used, e.g., in the following manner:

 % This makes a hexagonal lattice, where the units are rectangular
 % instead of hexagons.
    som_cplane('rect',som_vis_coords('hexa',[10 7]),'none');

 % Let's make a map and calculate a u-matrix: 
    sM=som_make(data,'msize',[10 7],'lattice','hexa');
    u=som_umat(sM); u=u(:);
 % Now, these produce equivalent results:
    som_cplane('hexaU',[10 7],u);
    som_cplane(vis_patch('hexa')/2,som_vis_coords('hexaU',[10 7]),u);

See also