findTransects

FINDTRANSECTS  Identify transects from waypoint coordinates.

  Syntax:
    TRANSECT_INDEX = FINDTRANSECTS(WAYPOINT_LATITUDE, WAYPOINT_LONGITUDE)

  Description:
    TRANSECT_INDEX = FINDTRANSECTS(WAYPOINT_LATITUDE, WAYPOINT_LONGITUDE) 
    identifies transects (travels from one waypoint to the next one) from 
    waypoint coordinates in vectors WAYPOINT_LATITUDE and WAIPONT_LONGITUDE, 
    and flags each point with the index of the transect the point belongs to, 
    starting from 1. WAYPOINT_LATITUDE, WAYPOINT_LONGITUDE and TRANSECT_INDEX
    have the same length.

  Notes:
    A new transect starts whenever a change in latitude or longitude waypoint
    coordinate is found. Transects are numbered cumulating changes of latitude 
    or longitude coordinates, ignoring invalid values (NaN) in the sequences.

    This function is based on the previous work by Tomeu Garau, in a function
    called GETTRANSECTS. He is the true glider man.

  Examples:
    waypoint_latitude  = [39.50   nan 39.50  nan 39.21   nan 39.23   nan   nan   nan 38.98   nan 38.98]
    waypoint_longitude = [ 2.18   nan   nan  nan  1.65   nan  1.28   nan  1.09   nan  1.09   nan  0.12]
    transect_index = findTransects(waypoint_latitude, waypoint_longitude)
    figure
    subplot(2,1,1)
    plotyy(waypoint_latitude, 'og', waypoint_longitude, 'or')
    subplot(2,1,2)
    stairs(transect_index)

  Authors:
    Joan Pau Beltran  <joanpau.beltran@socib.cat>

0001 function transect_index = findTransects(waypoint_latitude, waypoint_longitude)
0002 %FINDTRANSECTS  Identify transects from waypoint coordinates.
0003 %
0004 %  Syntax:
0005 %    TRANSECT_INDEX = FINDTRANSECTS(WAYPOINT_LATITUDE, WAYPOINT_LONGITUDE)
0006 %
0007 %  Description:
0008 %    TRANSECT_INDEX = FINDTRANSECTS(WAYPOINT_LATITUDE, WAYPOINT_LONGITUDE)
0009 %    identifies transects (travels from one waypoint to the next one) from
0010 %    waypoint coordinates in vectors WAYPOINT_LATITUDE and WAIPONT_LONGITUDE,
0011 %    and flags each point with the index of the transect the point belongs to,
0012 %    starting from 1. WAYPOINT_LATITUDE, WAYPOINT_LONGITUDE and TRANSECT_INDEX
0013 %    have the same length.
0014 %
0015 %  Notes:
0016 %    A new transect starts whenever a change in latitude or longitude waypoint
0017 %    coordinate is found. Transects are numbered cumulating changes of latitude
0018 %    or longitude coordinates, ignoring invalid values (NaN) in the sequences.
0019 %
0020 %    This function is based on the previous work by Tomeu Garau, in a function
0021 %    called GETTRANSECTS. He is the true glider man.
0022 %
0023 %  Examples:
0024 %    waypoint_latitude  = [39.50   nan 39.50  nan 39.21   nan 39.23   nan   nan   nan 38.98   nan 38.98]
0025 %    waypoint_longitude = [ 2.18   nan   nan  nan  1.65   nan  1.28   nan  1.09   nan  1.09   nan  0.12]
0026 %    transect_index = findTransects(waypoint_latitude, waypoint_longitude)
0027 %    figure
0028 %    subplot(2,1,1)
0029 %    plotyy(waypoint_latitude, 'og', waypoint_longitude, 'or')
0030 %    subplot(2,1,2)
0031 %    stairs(transect_index)
0032 %
0033 %  Authors:
0034 %    Joan Pau Beltran  <joanpau.beltran@socib.cat>
0035 
0036 %  Copyright (C) 2013-2016
0037 %  ICTS SOCIB - Servei d'observacio i prediccio costaner de les Illes Balears
0038 %  <http://www.socib.es>
0039 %
0040 %  This program is free software: you can redistribute it and/or modify
0041 %  it under the terms of the GNU General Public License as published by
0042 %  the Free Software Foundation, either version 3 of the License, or
0043 %  (at your option) any later version.
0044 %
0045 %  This program is distributed in the hope that it will be useful,
0046 %  but WITHOUT ANY WARRANTY; without even the implied warranty of
0047 %  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
0048 %  GNU General Public License for more details.
0049 %
0050 %  You should have received a copy of the GNU General Public License
0051 %  along with this program.  If not, see <http://www.gnu.org/licenses/>.
0052 
0053   error(nargchk(2, 2, nargin, 'struct'));
0054   
0055   waypoint_coordinates = [waypoint_latitude(:) waypoint_longitude(:)];
0056   
0057   % Initialize transect index to have the same dimensions as given inputs.
0058   % This also handles degenerated cases (empty or all data invalid).
0059   transect_index = ones(size(waypoint_latitude)); 
0060   if ~isempty(waypoint_coordinates)
0061     waypoint_coordinate_change = false(size(waypoint_coordinates));
0062     for i = 1:2
0063       coord_valid_sel = ~isnan(waypoint_coordinates(:,i));
0064       coord_valid_ind = find(coord_valid_sel);
0065       coord_valid = waypoint_coordinates(coord_valid_sel, i);
0066       coord_valid_change = [false; (coord_valid(2:end) ~= coord_valid(1:end-1))];
0067       waypoint_coordinate_change(coord_valid_ind(coord_valid_change), i) = true;
0068     end
0069     transect_index(:) = 1 + cumsum(any(waypoint_coordinate_change, 2));   
0070   end
0071   
0072 end