Plotting non-gridded vectorial data on a map

Hello,

I would like to plot the evolution of wind velocity along the trajectory of a drifting buoy. I have the following variables:

lon [N x 1] vector: longitude at the N locations transmitted by the buoy [degrees east]

lat [N x 1] vector: latitude at the N locations transmitted by the buoy [degrees north]

uwind [N x 1] vector: u-component of the wind velocity at the N locations transmitted by the buoy [m/s]

vwind [N x 1] vector: v-component of the wind velocity at the N locations transmitted by the buoy [m/s]

I have tried the following:

figure; hold on;

plot (lon, lat, 'k.'); % Plot buoy trajectory

axis equal; axis([min(lon)-.02, max(lon)+.02, min(lat)-.02, max(lat)+.02]); % Set axis limits

quiverwcolorbar(lon, lat, uwind, vwind, 0.0025, 'bounds', [3 12]); % Arrow plot

title('Wind speed (m/s)');

I could have used "quiver" instead of "quiverwcolorbar". This figure (attached) is fine, but I am not using any specific map projection and I am not sure about whether the vectors are pointing to the right direction. For example, if I use "axis equal", both the longitude and the latitude axis will share the same scaling, but I feel this is not correct since a change of 1º in the east-west direction does not involve the same displacement (e.g. in miles or kilometers) as a change of 1º in the north-south direction.

So, I moved to the MATLAB Mapping Toolbox and tried the following code:

figure; hold on; H = worldmap([min(lat)-.02, max(lat)+.02], [min(lon)-.02, max(lon)+.02]);

setm(H, 'MapProjection', 'mercator'); % Using a conformal, angle-preserving projection

quiverwcolorbar(lon, lat, uwind, vwind, 0.0025, 'bounds', [3 12]); % Arrow plot

However, it doesn't work, no matter I use the "quiver" function or the "quiverwcolorbar" function. No error is returned, but I can't see the arrows on the map. So, I tried using quivermc:

figure; hold on; H = worldmap([min(lat)-.02, max(lat)+.02], [min(lon)-.02, max(lon)+.02]);

setm(H, 'MapProjection', 'mercator'); % Using a conformal, angle-preserving projection

quivermc(lat, lon, uwind, vwind);

But the following error is returned:

??? Error using ==> quivermc at 145 Input lat, lon, u, and v must be a grid.

I'm working with non-gridded data, since my data don't come from an eulerian field, but from positions along the path of a drifing buoy. Perhaps I can write my data into a grid, with:

slon = sort(lon, ‘ascend’); slat = sort(lat, ‘ascend’);

[LON, LAT] = meshgrid(slon,slat); % Creates LON [N x N] and LAT [N x N] arrays

UWIND = nan(size(LON)); VWIND = nan(size(LAT));

for i=1:N

     lon_i = lon(i); lat_i = lat(i); % longitude and latitude in this iteration

     uwind_i = uwind(i); vwind_i = vwind(i); % u-wind and v-wind in this iteration

     lonIdx = find(slon == lon_i); latIdx = find(slat == lat_i); % find longitude and latitude indexes

     UWIND(lonIdx, latIdx) = uwind_i; VWIND(lonIdx, latIdx) = vwind_i; % write wind data into a gridded format

end

figure; hold on; H = worldmap([min(lat)-.02, max(lat)+.02], [min(lon)-.02, max(lon)+.02]);

setm(H, 'MapProjection', 'mercator'); % Using a conformal, angle-preserving projection

quivermc(LAT, LON, UWIND, VWIND);

No error is returned. However, although I'm working with gridded data now, I can't see the arrows on the map, just a few scattered points. What am I doing wrong? Is there any MATLAB function to plot non-gridded vectorial data using a Map Projection?

Thank you.

[Oscar Petlund]

I am having the exact same issue. Did you find a solution?