Wrong patch using the Faces and Vertices properties when projected on map (patchm)

I am trying to color lines by a specific value using patch and patchm where I use vertices and faces (my faces are actually only lines with a start and end point). The lines connect some station pairs, i.e. station 1 with station 2, station 1 with station 3, etc. Each station pair is defined by latitude and longitude and stored in the variable verts.

 verts(1:10,:)

 ans =

   63.4946    9.7362
   62.7815    7.1518
   63.4946    9.7362
   62.7836    8.8780
   63.4946    9.7362
   62.7205   10.0433
   63.4946    9.7362
   62.5622   11.5530
   63.4946    9.7362
   62.1345    5.9689

The specific values for the station pairs are stored in the variable cohmap.

 cohmap(1:10)

 ans =

    0.9318
    0.9318
    1.0166
    1.0166
    1.0346
    1.0346
    1.1186
    1.1186
    1.0251
    1.0251

When I use a simple x,y plot using patch everything works out correctly. The correct station pairs are connected and colored by their correct values.

 fac=[1:2:10; 2:2:10]';   p=patch('Faces',fac,'Vertices',verts,'FaceColor','none','EdgeColor','flat', 'LineWidth',1);
 set(gca,'CLim',[0 1]);
 colormap(jet);
 set(p,'FaceColor','flat','FaceVertexCData',cohmap,'CDataMapping','scaled')
 colorbar

 for snm = 1:length(stlas)
    plot(stlos(snm), stlas(snm), 'k^', 'MarkerFaceColor', 'k');
 end

However, when I try to project the patch to a map using patchm I get this result:

 ax = worldmap([57 64], [4 14]);
 set(ax, 'Visible', 'on', 'FontSize',8)    
 setm(gca,'FLineWidth',1, 'fontsize', 4, 'LabelFormat', 'none', 'MLineLocation', 3,  'PLineLocation', 3, 'MLabelLocation', [6 9 12 15], 'PLabelLocation', [57 60 63], 'MLabelRound',  0, 'PLabelRound', 0);
 p = patchm(verts(:, 1), verts(:, 2), 'Faces', fac, 'FaceColor','none','EdgeColor','flat',  'LineWidth',2, 'FaceVertexCData',cohmap,'CDataMapping','scaled');
 set(gca,'CLim',[0 1]);
 colormap(jet);
 colorbar

 for snm = 1:length(stlas)
        plotm(stlas(snm), stlos(snm), 'k^', 'MarkerFaceColor', 'k');
 end

 borderN = shaperead('/path/NOR_adm0.shp', 'UseGeoCoords', true);
 borderS = shaperead('/path/SWE_adm0.shp', 'UseGeoCoords', true);
 geoshow(borderN.Lat, borderN.Lon, 'Color', [0.66, 0.66, 0.66],'linewidth', 0.5)
 geoshow(borderS.Lat, borderS.Lon, 'Color', [0.66, 0.66, 0.66],'linewidth', 0.5)

Obviously, using patchm wrong station pairs are used. What is going wrong here? Why I get this using patchm?

Answer 1

[Kelly Kearney]

Last I checked, patchm doesn't accept face/vertex input data... (which is a pain in the ass, because plotting triangulated patches is often the only way to properly render complex polygons with holes (like, say, land).

As a workaround, I do the face/vertex expansion manaually. This will give you the proper connections:

verts = [...
   63.4946    9.7362
   62.7815    7.1518
   63.4946    9.7362
   62.7836    8.8780
   63.4946    9.7362
   62.7205   10.0433
   63.4946    9.7362
   62.5622   11.5530
   63.4946    9.7362
   62.1345    5.9689];

cohmap = [...
    0.9318
    0.9318
    1.0166
    1.0166
    1.0346
    1.0346
    1.1186
    1.1186
    1.0251
    1.0251];

fac = [1:2:10; 2:2:10]'; 

vlon = verts(:,2);
vlat = verts(:,1);
lat = vlat(fac);
lon = vlon(fac);

c = cohmap(fac);

ax = worldmap([57 64], [4 14]);
h = patchm(lat', lon', 'r');

But... not the right color, since I've never been able to get mapped patches to interpret edge color correctly. For that, I find you need to plot each line/patch independently, and explicitly set the edge color to an RGB value:

for ii = 1:size(lon,1)
    h(ii) = patchm(lat(ii,:), lon(ii,:), 'k');
end

clims = [min(cohmap) max(cohmap)];
col = interpcolor(cohmap, jet(), [0 1]);
set(h, {'edgecolor'}, num2cell(col(1:5,:),2));

(Find interpcolor here)

[Colibri]

Thank you very much! Your workaround did the job. Thanks for providing it for the community.

Answer 2

[Chad Greene]

I've had similar problems with patchm before. I'm not sure why it helped in my particular case, but the fix I found was to flip the arrays of lats and lons, like this:

p = patchm(flipud(verts(:, 1)),flipud(verts(:, 2)),...

No guarantee that it'll work, but give it might be worth a shot.

[Colibri]

Unfortunately, that did not work for me. Would have been too good to be true ... Maybe it depends on the matlab version you are using? I use the 2012a one.